【程序1】
题目:古典问题:有一对兔子,从出生后第3个月起每个月都生一对兔子,小兔子长到第三个月后每个月又生一对兔子,假如兔子都不死,问每个月的兔子总数为多少?
程序分析: 兔子的规律为数列1,1,2,3,5,8,13,21....
package com.example.lib;/*
题目:古典问题:有一对兔子,从出生后第3个月起每个月都生一对兔子,小兔子长到第三个月后每个月又生一对兔子,
假如兔子都不死,问每个月的兔子总数为多少?
程序分析: 兔子的规律为数列1,1,2,3,5,8,13,21....
* */
public class Prog1 {public static void main(String[] args) {int n = 4;System.out.println("第" + n + "个月兔子总数为" + 2 * fun(n));}private static int fun(int n) {if (n == 1 || n == 2)return 1;elsereturn fun(n - 1) + fun(n - 2);}
}
【程序2】
题目:判断101-200之间有多少个素数,并输出所有素数。
程序分析:判断素数的方法:用一个数分别去除2到sqrt(这个数),如果能被整除,则表明此数不是素数,反之是素数。
package com.example.lib;/*
题目:判断101-200之间有多少个素数,并输出所有素数。
程序分析:判断素数的方法:用一个数分别去除2到sqrt(这个数),如果能被整除,则表明此数不是素数,反之是素数。
* */
public class Prog2 {public static void main(String[] args) {int m = 1;int n = 1000;int count = 0;//统计素数个数for (int i = m; i < n; i++) {if (isPrime(i)) {count++;System.out.print(i + " ");if (count % 10 == 0) {System.out.println();}}}System.out.println();System.out.println("在" + m + "和" + n + "之间共有" + count + "个素数");}//判断素数private static boolean isPrime(int n) {boolean flag = true;if (n == 1) {flag = false;} else {for (int i = 2; i <= Math.sqrt(n); i++) {if ((n % i) == 0 || n == 1) {flag = false;break;}}}return flag;}
}
【程序3】
题目:打印出所有的"水仙花数",所谓"水仙花数"是指一个三位数,其各位数字立方和等于该数本身。例如:153是一个"水仙花数",因为153=1的三次方+5的三次方+3的三次方。
程序分析:利用for循环控制100-999个数,每个数分解出个位,十位,百位。
package com.example.lib;/*题目:打印出所有的"水仙花数",所谓"水仙花数"是指一个三位数,其各位数字立方和等于该数本身。
例如:153是一个"水仙花数",因为153=1的三次方+5的三次方+3的三次方。
程序分析:利用for循环控制100-999个数,每个数分解出个位,十位,百位。
* */
public class Prog3 {public static void main(String[] args) {for (int i = 100; i < 1000; i++) {if (isLotus(i))System.out.print(i + " ");}System.out.println();}//判断水仙花数private static boolean isLotus(int lotus) {int m = 0;int n = lotus;int sum = 0;m = n / 100;n -= m * 100;sum = m * m * m;m = n / 10;n -= m * 10;sum += m * m * m + n * n * n;if (sum == lotus)return true;elsereturn false;}
}
【程序4】
package com.example.lib;/*
题目:将一个正整数分解质因数。例如:输入90,打印出90=2*3*3*5。
程序分析:对n进行分解质因数,应先找到一个最小的质数k,然后按下述步骤完成:
(1)如果这个质数恰等于n,则说明分解质因数的过程已经结束,打印出即可。
(2)如果n<>k,但n能被k整除,则应打印出k的值,并用n除以k的商,作为新的正整数n,重复执行第一步。
(3)如果n不能被k整除,则用k+1作为k的值,重复执行第一步。
*/
public class Prog4 {public static void main(String[] args) {int n = 13;decompose(n);}private static void decompose(int n) {System.out.print(n + "=");for (int i = 2; i < n + 1; i++) {while (n % i == 0 && n != i) {n /= i;System.out.print(i + "*");}if (n == i) {System.out.println(i);break;}}}
}
【
package com.example.lib;程序5】题目:利用条件运算符的嵌套来完成此题:学习成绩>=90分的同学用A表示,60-89分之间的用B表示,60分以下的用C表示。程序分析:(a>b)?a:b这是条件运算符的基本例子。public class Prog5 {public static void main(String[] args) {int n = -1;try {n = Integer.parseInt(args[0]);} catch (ArrayIndexOutOfBoundsException e) {System.out.println("请输入成绩");return;}grade(n);}//成绩等级计算private static void grade(int n) {if (n > 100 || n < 0)System.out.println("输入无效");else {String str = (n >= 90) ? "分,属于A等" : ((n > 60) ? "分,属于B等" : "分,属于C等");System.out.println(n + str);}} }【程序6】题目:输入两个正整数m和n,求其最大公约数和最小公倍数。程序分析:利用辗除法。public class Prog6 {public static void main(String[] args) {int m, n;try {m = Integer.parseInt(args[0]);n = Integer.parseInt(args[1]);} catch (ArrayIndexOutOfBoundsException e) {System.out.println("输入有误");return;}max_min(m, n);}//求最大公约数和最小公倍数private static void max_min(int m, int n) {int temp = 1;int yshu = 1;int bshu = m * n;if (n < m) {temp = n;n = m;m = temp;}while (m != 0) {temp = n % m;n = m;m = temp;}yshu = n;bshu /= n;System.out.println(m + "和" + n + "的最大公约数为" + yshu);System.out.println(m + "和" + n + "的最小公倍数为" + bshu);} }【程序7】题目:输入一行字符,分别统计出其中英文字母、空格、数字和其它字符的个数。程序分析:利用while语句,条件为输入的字符不为'\n'.import java.util.Scanner;public class Prog7_1 {public static void main(String[] args) {System.out.print("请输入一串字符:");Scanner scan = new Scanner(System.in);String str = scan.nextLine();//将一行字符转化为字符串scan.close();count(str);}//统计输入的字符数private static void count(String str) {String E1 = "[\u4e00-\u9fa5]";//汉字String E2 = "[a-zA-Z]";String E3 = "[0-9]";String E4 = "\\s";//空格int countChinese = 0;int countLetter = 0;int countNumber = 0;int countSpace = 0;int countOther = 0;char[] array_Char = str.toCharArray();//将字符串转化为字符数组String[] array_String = new String[array_Char.length];//汉字只能作为字符串处理for (int i = 0; i < array_Char.length; i++)array_String[i] = String.valueOf(array_Char[i]);//遍历字符串数组中的元素for (String s : array_String) {if (s.matches(E1))countChinese++;else if (s.matches(E2))countLetter++;else if (s.matches(E3))countNumber++;else if (s.matches(E4))countSpace++;elsecountOther++;}System.out.println("输入的汉字个数:" + countChinese);System.out.println("输入的字母个数:" + countLetter);System.out.println("输入的数字个数:" + countNumber);System.out.println("输入的空格个数:" + countSpace);System.out.println("输入的其它字符个数:" + countSpace);}}import java.util.*;public class Prog7_2 {public static void main(String[] args) {System.out.println("请输入一行字符:");Scanner scan = new Scanner(System.in);String str = scan.nextLine();scan.close();count(str);}//统计输入的字符private static void count(String str) {List<String> list = new ArrayList<String>();char[] array_Char = str.toCharArray();for (char c : array_Char)list.add(String.valueOf(c));//将字符作为字符串添加到list表中Collections.sort(list);//排序for (String s : list) {int begin = list.indexOf(s);int end = list.lastIndexOf(s);//索引结束统计字符数if (list.get(end) == s)System.out.println("字符‘" + s + "’有" + (end - begin + 1) + "个");}}}【程序8】题目:求s=a+aa+aaa+aaaa+aa...a的值,其中a是一个数字。例如2+22+222+2222+22222(此时共有5个数相加),几个数相加有键盘控制。程序分析:关键是计算出每一项的值。import java.util.Scanner;public class Prog8 {public static void main(String[] args) {System.out.print("求s=a+aa+aaa+aaaa+...的值,请输入a的值:");Scanner scan = new Scanner(System.in).useDelimiter("\\s*");//以空格作为分隔符int a = scan.nextInt();int n = scan.nextInt();scan.close();//关闭扫描器System.out.println(expressed(2, 5) + add(2, 5));}//求和表达式private static String expressed(int a, int n) {StringBuffer sb = new StringBuffer();StringBuffer subSB = new StringBuffer();for (int i = 1; i < n + 1; i++) {subSB = subSB.append(a);sb = sb.append(subSB);if (i < n)sb = sb.append("+");}sb.append("=");return sb.toString();}//求和private static long add(int a, int n) {long sum = 0;long subSUM = 0;for (int i = 1; i < n + 1; i++) {subSUM = subSUM * 10 + a;sum = sum + subSUM;}return sum;}}【程序9】题目:一个数如果恰好等于它的因子之和,这个数就称为"完数"。例如6=1+2+3.编程找出1000以内的所有完数。public class Prog9 {public static void main(String[] args) {int n = 10000;compNumber(n);}//求完数private static void compNumber(int n) {int count = 0;System.out.println(n + "以内的完数:");for (int i = 1; i < n + 1; i++) {int sum = 0;for (int j = 1; j < i / 2 + 1; j++) {if ((i % j) == 0) {sum += j;if (sum == i) {System.out.print(i + " ");if ((count++) % 5 == 0)System.out.println();}}}}}}【程序10】题目:一球从100米高度自由落下,每次落地后反跳回原高度的一半;再落下,求它在 第10次落地时,共经过多少米?第10次反弹多高?import java.util.Scanner;public class Prog10 {public static void main(String[] args) {System.out.print("请输入小球落地时的高度和求解的次数:");Scanner scan = new Scanner(System.in).useDelimiter("\\s");int h = scan.nextInt();int n = scan.nextInt();scan.close();distance(h, n);}//小球从h高度落下,经n次反弹后经过的距离和反弹的高度private static void distance(int h, int n) {double length = 0;for (int i = 0; i < n; i++) {length += h;h /= 2.0;}System.out.println("经过第" + n + "次反弹后,小球共经过" + length + "米," + "第" + n + "次反弹高度为" + h + "米");}}【程序11】题目:有1、2、3、4个数字,能组成多少个互不相同且无重复数字的三位数?都是多少?程序分析:可填在百位、十位、个位的数字都是1、2、3、4。组成所有的排列后再去 掉不满足条件的排列。public class Prog11 {public static void main(String[] args) {int count = 0;int n = 0;for (int i = 1; i < 5; i++) {for (int j = 1; j < 5; j++) {if (j == i)continue;for (int k = 1; k < 5; k++) {if (k != i && k != j) {n = i * 100 + j * 10 + k;System.out.print(n + " ");if ((++count) % 5 == 0)System.out.println();}}}}System.out.println();System.out.println("符合条件的数共:" + count + "个");}}【程序12】题目:企业发放的奖金根据利润提成。利润(I)低于或等于10万元时,奖金可提10%;利润高于10万元,低于20万元时,低于10万元的部分按10%提成,高于10万元的部分,可可提成7.5%;20万到40万之间时,高于20万元的部分,可提成5%;40万到60万之间时高于40万元的部分,可提成3%;60万到100万之间时,高于60万元的部分,可提成1.5%,高于100万元时,超过100万元的部分按1%提成,从键盘输入当月利润I,求应发放奖金总数?程序分析:请利用数轴来分界,定位。注意定义时需把奖金定义成长整型。import java.io.*;public class Prog12 {public static void main(String[] args) {System.out.print("请输入当前利润:");long profit = Long.parseLong(key_Input());System.out.println("应发奖金:" + bonus(profit));}//接受从键盘输入的内容private static String key_Input() {String str = null;BufferedReader bufIn = new BufferedReader(new InputStreamReader(System.in));try {str = bufIn.readLine();} catch (IOException e) {e.printStackTrace();} finally {try {bufIn.close();} catch (IOException e) {e.printStackTrace();}}return str;}//计算奖金private static long bonus(long profit) {long prize = 0;long profit_sub = profit;if (profit > 1000000) {profit = profit_sub - 1000000;profit_sub = 1000000;prize += profit * 0.01;}if (profit > 600000) {profit = profit_sub - 600000;profit_sub = 600000;prize += profit * 0.015;}if (profit > 400000) {profit = profit_sub - 400000;profit_sub = 400000;prize += profit * 0.03;}if (profit > 200000) {profit = profit_sub - 200000;profit_sub = 200000;prize += prize * 0.05;}if (profit > 100000) {profit = profit_sub - 100000;profit_sub = 100000;prize += profit * 0.075;}prize += profit_sub * 0.1;return prize;}}【程序13】题目:一个整数,它加上100后是一个完全平方数,再加上168又是一个完全平方数,请问该数是多少?程序分析:在10万以内判断,先将该数加上100后再开方,再将该数加上268后再开方,如果开方后的结果满足如下条件,即是结果。public class Prog13 {public static void main(String[] args) {int n = 0;for (int i = 0; i < 100001; i++) {if (isCompSqrt(i + 100) && isCompSqrt(i + 268)) {n = i;break;}}System.out.println("所求的数是:" + n);}//判断完全平方数private static boolean isCompSqrt(int n) {boolean isComp = false;for (int i = 1; i < Math.sqrt(n) + 1; i++) {if (n == Math.pow(i, 2)) {isComp = true;break;}}return isComp;}}【程序14】题目:输入某年某月某日,判断这一天是这一年的第几天?程序分析:以3月5日为例,应该先把前两个月的加起来,然后再加上5天即本年的第几天,特殊情况,闰年且输入月份大于3时需考虑多加一天。import java.util.Scanner;public class Prog14 {public static void main(String[] args) {Scanner scan = new Scanner(System.in).useDelimiter("\\D");//匹配非数字System.out.print("请输入当前日期(年-月-日):");int year = scan.nextInt();int month = scan.nextInt();int date = scan.nextInt();scan.close();System.out.println("今天是" + year + "年的第" + analysis(year, month, date) + "天");}//判断天数private static int analysis(int year, int month, int date) {int n = 0;int[] month_date = new int[]{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30};if ((year % 400) == 0 || ((year % 4) == 0) && ((year % 100) != 0))month_date[2] = 29;for (int i = 0; i < month; i++)n += month_date[i];return n + date;}}【程序15】题目:输入三个整数x,y,z,请把这三个数由小到大输出。程序分析:我们想办法把最小的数放到x上,先将x与y进行比较,如果x>y则将x与y的值进行交换,然后再用x与z进行比较,如果x>z则将x与z的值进行交换,这样能使x最小。import java.util.Scanner;public class Prog15 {public static void main(String[] args) {Scanner scan = new Scanner(System.in).useDelimiter("\\D");System.out.print("请输入三个数:");int x = scan.nextInt();int y = scan.nextInt();int z = scan.nextInt();scan.close();System.out.println("排序结果:" + sort(x, y, z));}//比较两个数的大小private static String sort(int x, int y, int z) {String s = null;if (x > y) {int t = x;x = y;y = t;}if (x > z) {int t = x;x = z;z = t;}if (y > z) {int t = z;z = y;y = t;}s = x + " " + y + " " + z;return s;}}【程序16】题目:输出9*9口诀。程序分析:分行与列考虑,共9行9列,i控制行,j控制列。public class Prog16 {public static void main(String[] args) {for (int i = 1; i < 10; i++) {for (int j = 1; j < i + 1; j++)System.out.print(j + "*" + i + "=" + (j * i) + " ");System.out.println();}}}【程序17】题目:猴子吃桃问题:猴子第一天摘下若干个桃子,当即吃了一半,还不瘾,又多吃了一个 第二天早上又将剩下的桃子吃掉一半,又多吃了一个。以后每天早上都吃了前一天剩下的一半零一个。到第10天早上想再吃时,见只剩下一个桃子了。求第一天共摘了多少。程序分析:采取逆向思维的方法,从后往前推断。public class Prog17 {public static void main(String[] args) {int m = 1;for (int i = 10; i > 0; i--)m = 2 * m + 2;System.out.println("小猴子共摘了" + m + "桃子");}} 【程序18】题目:两个乒乓球队进行比赛,各出三人。甲队为a,b,c三人,乙队为x,y,z三人。已抽签决定比赛名单。有人向队员打听比赛的名单。a说他不和x比,c说他不和x,z比,请编程序找出三队赛手的名单。import java.util.ArrayList;public class Prog18 {String a, b, c;//甲队成员public static void main(String[] args) {String[] racer = {"x", "y", "z"};//乙队成员ArrayList<Prog18> arrayList = new ArrayList<Prog18>();for (int i = 0; i < 3; i++)for (int j = 0; j < 3; j++)for (int k = 0; k < 3; k++) {Prog18 prog18 = new Prog18(racer[i], racer[j], racer[k]);if (!prog18.a.equals(prog18.b) && !prog18.a.equals(prog18.c) && !prog18.b.equals(prog18.c) &&!prog18.a.equals("x") && !prog18.c.equals("x") && !prog18.c.equals("z"))arrayList.add(prog18);}for (Object obj : arrayList)System.out.println(obj);}//构造方法private Prog18(String a, String b, String c) {this.a = a;this.b = b;this.c = c;}public String toString() {return "a的对手是" + a + " " + "b的对手是" + b + " " + "c的对手是" + c;}}【程序19】题目:打印出如下图案(菱形)****************************程序分析:先把图形分成两部分来看待,前四行一个规律,后三行一个规律,利用双重 for循环,第一层控制行,第二层控制列。public class Prog19 {public static void main(String[] args) {int n = 5;printStar(n);}//打印星星private static void printStar(int n) {//打印上半部分for (int i = 0; i < n; i++) {for (int j = 0; j < 2 * n; j++) {if (j < n - i)System.out.print(" ");if (j >= n - i && j <= n + i)System.out.print("*");}System.out.println();}//打印下半部分for (int i = 1; i < n; i++) {System.out.print(" ");for (int j = 0; j < 2 * n - i; j++) {if (j < i)System.out.print(" ");if (j >= i && j < 2 * n - i - 1)System.out.print("*");}System.out.println();}}}【程序20】题目:有一分数序列:2/1,3/2,5/3,8/5,13/8,21/13...求出这个数列的前20项之和。程序分析:请抓住分子与分母的变化规律。public class Prog20 {public static void main(String[] args) {double n1 = 1;double n2 = 1;double fraction = n1 / n2;double Sn = 0;for (int i = 0; i < 20; i++) {double t1 = n1;double t2 = n2;n1 = t1 + t2;n2 = t1;fraction = n1 / n2;Sn += fraction;}System.out.print(Sn);}}【程序21】题目:求1+2!+3!+...+20!的和程序分析:此程序只是把累加变成了累乘。public class Prog21 {public static void main(String[] args) {long sum = 0;for (int i = 0; i < 20; i++)sum += factorial(i + 1);System.out.println(sum);}//阶乘private static long factorial(int n) {int mult = 1;for (int i = 1; i < n + 1; i++)mult *= i;return mult;}}【程序22】题目:利用递归方法求5!。程序分析:递归公式:fn=fn_1*4!public class Prog22 {public static void main(String[] args) {System.out.println(fact(10));}//递归求阶乘private static long fact(int n) {if (n == 1)return 1;elsereturn fact(n - 1) * n;}}【程序23】题目:有5个人坐在一起,问第五个人多少岁?他说比第4个人大2岁。问第4个人岁数,他说比第3个人大2岁。问第三个人,又说比第2人大两岁。问第2个人,说比第一个人大两岁。最后问第一个人,他说是10岁。请问第五个人多大?程序分析:利用递归的方法,递归分为回推和递推两个阶段。要想知道第五个人岁数,需知道第四人的岁数,依次类推,推到第一人(10岁),再往回推。public class Prog23 {public static void main(String[] args) {System.out.println(getAge(5, 2));}//求第m位同志的年龄private static int getAge(int m, int n) {if (m == 1)return 10;elsereturn getAge(m - 1, n) + n;}}【程序24】题目:给一个不多于5位的正整数,要求:一、求它是几位数,二、逆序打印出各位数字。public class Prog24 {public static void main(String[] args) {int n = Integer.parseInt(args[0]);int i = 0;int[] a = new int[5];do {a[i] = n % 10;n /= 10;++i;} while (n != 0);System.out.print("这是一个" + i + "位数,从个位起,各位数字依次为:");for (int j = 0; j < i; j++)System.out.print(a[j] + " ");}}【程序25】题目:一个5位数,判断它是不是回文数。即12321是回文数,个位与万位相同,十位与千位相同。import java.io.*;public class Prog25 {public static void main(String[] args) {int n = 0;System.out.print("请输入一个5位数:");BufferedReader bufin = new BufferedReader(new InputStreamReader(System.in));try {n = Integer.parseInt(bufin.readLine());} catch (IOException e) {e.printStackTrace();} finally {try {bufin.close();} catch (IOException e) {e.printStackTrace();}}palin(n);}private static void palin(int n) {int m = n;int[] a = new int[5];if (n < 10000 || n > 99999) {System.out.println("输入的不是5位数!");return;} else {for (int i = 0; i < 5; i++) {a[i] = n % 10;n /= 10;}if (a[0] == a[4] && a[1] == a[3])System.out.println(m + "是一个回文数");elseSystem.out.println(m + "不是回文数");}}}【程序26】题目:请输入星期几的第一个字母来判断一下是星期几,如果第一个字母一样,则继续 判断第二个字母。程序分析:用情况语句比较好,如果第一个字母一样,则判断用情况语句或if语句判断第二个字母。import java.io.*;public class Prog26 {public static void main(String[] args) {String str = new String();BufferedReader bufIn = new BufferedReader(new InputStreamReader(System.in));System.out.print("请输入星期的英文单词前两至四个字母):");try {str = bufIn.readLine();} catch (IOException e) {e.printStackTrace();} finally {try {bufIn.close();} catch (IOException e) {e.printStackTrace();}}week(str);}private static void week(String str) {int n = -1;if (str.trim().equalsIgnoreCase("Mo") || str.trim().equalsIgnoreCase("Mon") || str.trim().equalsIgnoreCase("Mond"))n = 1;if (str.trim().equalsIgnoreCase("Tu") || str.trim().equalsIgnoreCase("Tue") || str.trim().equalsIgnoreCase("Tues"))n = 2;if (str.trim().equalsIgnoreCase("We") || str.trim().equalsIgnoreCase("Wed") || str.trim().equalsIgnoreCase("Wedn"))n = 3;if (str.trim().equalsIgnoreCase("Th") || str.trim().equalsIgnoreCase("Thu") || str.trim().equalsIgnoreCase("Thur"))n = 4;if (str.trim().equalsIgnoreCase("Fr") || str.trim().equalsIgnoreCase("Fri") || str.trim().equalsIgnoreCase("Frid"))n = 5;if (str.trim().equalsIgnoreCase("Sa") || str.trim().equalsIgnoreCase("Sat") || str.trim().equalsIgnoreCase("Satu"))n = 2;if (str.trim().equalsIgnoreCase("Su") || str.trim().equalsIgnoreCase("Sun") || str.trim().equalsIgnoreCase("Sund"))n = 0;switch (n) {case 1:System.out.println("星期一");break;case 2:System.out.println("星期二");break;case 3:System.out.println("星期三");break;case 4:System.out.println("星期四");break;case 5:System.out.println("星期五");break;case 6:System.out.println("星期六");break;case 0:System.out.println("星期日");break;default:System.out.println("输入有误!");break;}}}【程序27】题目:求100之内的素数public class Prog27 {public static void main(String[] args) {int n = 100;System.out.print(n + "以内的素数:");for (int i = 2; i < n + 1; i++) {if (isPrime(i))System.out.print(i + " ");}}//求素数private static boolean isPrime(int n) {boolean flag = true;for (int i = 2; i < Math.sqrt(n) + 1; i++)if (n % i == 0) {flag = false;break;}return flag;}}【程序28】题目:对10个数进行排序程序分析:可以利用选择法,即从后9个比较过程中,选择一个最小的与第一个元素交换, 下次类推,即用第二个元素与后8个进行比较,并进行交换。public class Prog28 {public static void main(String[] args) {int[] a = new int[]{31, 42, 21, 50, 12, 60, 81, 74, 101, 93};for (int i = 0; i < 10; i++)for (int j = 0; j < a.length - i - 1; j++)if (a[j] > a[j + 1]) {int temp = a[j];a[j] = a[j + 1];a[j + 1] = temp;}for (int i = 0; i < a.length; i++)System.out.print(a[i] + " ");}}【程序29】题目:求一个3*3矩阵对角线元素之和程序分析:利用双重for循环控制输入二维数组,再将a[i][i]累加后输出。public class Prog29 {public static void main(String[] args) {int[][] a = new int[][]{{100, 2, 3,}, {4, 5, 6}, {17, 8, 9}};matrSum(a);}private static void matrSum(int[][] a) {int sum1 = 0;int sum2 = 0;for (int i = 0; i < a.length; i++)for (int j = 0; j < a[i].length; j++) {if (i == j) sum1 += a[i][j];if (j == a.length - i - 1) sum2 += a[i][j];}System.out.println("矩阵对角线之和分别是:" + sum1 + "和" + sum2);}}【程序30】题目:有一个已经排好序的数组。现输入一个数,要求按原来的规律将它插入数组中。程序分析:首先判断此数是否大于最后一个数,然后再考虑插入中间的数的情况,插入后此元素之后的数,依次后移一个位置。import java.util.Scanner;public class Prog30 {public static void main(String[] args) {int[] A = new int[]{0, 8, 7, 5, 9, 1, 2, 4, 3, 12};int[] B = sort(A);print(B);System.out.println();System.out.print("请输入10个数的数组:");Scanner scan = new Scanner(System.in);int a = scan.nextInt();scan.close();int[] C = insert(a, B);print(C);}//选择排序private static int[] sort(int[] A) {int[] B = new int[A.length];for (int i = 0; i < A.length - 1; i++) {int min = A[i];for (int j = i + 1; j < A.length; j++) {if (min > A[j]) {int temp = min;min = A[j];A[j] = temp;}B[i] = min;}}B[A.length - 1] = A[A.length - 1];return B;}//打印private static void print(int[] A) {for (int i = 0; i < A.length; i++)System.out.print(A[i] + " ");}//插入数字private static int[] insert(int a, int[] A) {int[] B = new int[A.length + 1];for (int i = A.length - 1; i > 0; i--)if (a > A[i]) {B[i + 1] = a;for (int j = 0; j <= i; j++)B[j] = A[j];for (int k = i + 2; k < B.length; k++)B[k] = A[k - 1];break;}return B;}}【程序31】题目:将一个数组逆序输出。程序分析:用第一个与最后一个交换。public class Prog31 {public static void main(String[] args) {int[] A = new int[]{1, 2, 3, 4, 5, 6, 7, 8, 9,};print(A);System.out.println();int[] B = reverse(A);print(B);}private static int[] reverse(int[] A) {for (int i = 0; i < A.length / 2; i++) {int temp = A[A.length - i - 1];A[A.length - i - 1] = A[i];A[i] = temp;}return A;}private static void print(int[] A) {for (int i = 0; i < A.length; i++)System.out.print(A[i] + " ");}}【程序32】题目:取一个整数a从右端开始的4~7位。程序分析:可以这样考虑:(1)先使a右移4位。(2)设置一个低4位全为1,其余全为0的数。可用~(~0<<4)(3)将上面二者进行&运算。import java.util.Scanner;public class Prog32 {public static void main(String[] msg) {//输入一个长整数Scanner scan = new Scanner(System.in);long l = scan.nextLong();scan.close();//以下截取字符String str = Long.toString(l);char[] ch = str.toCharArray();int n = ch.length;if (n < 7)System.out.println("输入的数小于7位!");elseSystem.out.println("截取的4~7位数字:" + ch[n - 7] + ch[n - 6] + ch[n - 5] + ch[n - 4]);}}【程序33】题目:打印出杨辉三角形(要求打印出10行如下图)程序分析:11 11 2 11 3 3 11 4 6 4 11 5 10 10 5 1public class Prog33 {public static void main(String[] args) {int[][] n = new int[10][21];n[0][10] = 1;for (int i = 1; i < 10; i++)for (int j = 10 - i; j < 10 + i + 1; j++)n[i][j] = n[i - 1][j - 1] + n[i - 1][j + 1];for (int i = 0; i < 10; i++) {for (int j = 0; j < 21; j++) {if (n[i][j] == 0)System.out.print(" ");else {if (n[i][j] < 10)System.out.print(" " + n[i][j]);//空格为了美观需要else if (n[i][j] < 100)System.out.print(" " + n[i][j]);elseSystem.out.print(n[i][j]);}}System.out.println();}}}【程序34】题目:输入3个数a,b,c,按大小顺序输出。程序分析:利用指针方法。import java.util.Scanner;public class Prog34 {public static void main(String[] args) {System.out.print("请输入3个数:");Scanner scan = new Scanner(System.in).useDelimiter("\\s");int a = scan.nextInt();int b = scan.nextInt();int c = scan.nextInt();scan.close();if (a < b) {int t = a;a = b;b = t;}if (a < c) {int t = a;a = c;c = t;}if (b < c) {int t = b;b = c;c = t;}System.out.println(a + " " + b + " " + c);}}【程序35】题目:输入数组,最大的与第一个元素交换,最小的与最后一个元素交换,输出数组。import java.util.Scanner;public class Prog35 {public static void main(String[] args) {System.out.print("请输入一组数:");Scanner scan = new Scanner(System.in).useDelimiter("\\s");int[] a = new int[50];int m = 0;while (scan.hasNextInt()) {a[m++] = scan.nextInt();}scan.close();int[] b = new int[m];for (int i = 0; i < m; i++)b[i] = a[i];for (int i = 0; i < b.length; i++)for (int j = 0; j < b.length - i - 1; j++)if (b[j] < b[j + 1]) {int temp = b[j];b[j] = b[j + 1];b[j + 1] = temp;}for (int i = 0; i < b.length; i++)System.out.print(b[i] + " ");}}【程序36】题目:有n个整数,使其前面各数顺序向后移m个位置,最后m个数变成最前面的m个数import java.util.Scanner;public class Prog36 {public static void main(String[] args) {final int N = 10;System.out.print("请输入10个数的数组:");Scanner scan = new Scanner(System.in);int[] a = new int[N];for (int i = 0; i < a.length; i++)a[i] = scan.nextInt();System.out.print("请输入一个小于10的数:");int m = scan.nextInt();scan.close();int[] b = new int[m];int[] c = new int[N - m];for (int i = 0; i < m; i++)b[i] = a[i];for (int i = m, j = 0; i < N; i++, j++)c[j] = a[i];for (int i = 0; i < N - m; i++)a[i] = c[i];for (int i = N - m, j = 0; i < N; i++, j++)a[i] = b[j];for (int i = 0; i < a.length; i++)System.out.print(a[i] + " ");}}【程序37】题目:有n个人围成一圈,顺序排号。从第一个人开始报数(从1到3报数),凡报到3的人退出圈子,问最后留下的是原来第几号的那位。import java.util.Scanner;public class Prog37 {public static void main(String[] args) {System.out.print("请输入一个整数:");Scanner scan = new Scanner(System.in);int n = scan.nextInt();scan.close();//定义数组变量标识某人是否还在圈内boolean[] isIn = new boolean[n];for (int i = 0; i < isIn.length; i++)isIn[i] = true;//定义圈内人数、报数、索引int inCount = n;int countNum = 0;int index = 0;while (inCount > 1) {if (isIn[index]) {countNum++;if (countNum == 3) {countNum = 0;isIn[index] = false;inCount--;}}index++;if (index == n)index = 0;}for (int i = 0; i < n; i++)if (isIn[i])System.out.println("留下的是:" + (i + 1));}}【程序38】题目:写一个函数,求一个字符串的长度,在main函数中输入字符串,并输出其长度。import java.util.Scanner;public class Prog38 {public static void main(String[] args) {System.out.print("请输入一串字符:");Scanner scan = new Scanner(System.in).useDelimiter("\\n");String strIn = scan.next();scan.close();char[] ch = strIn.toCharArray();System.out.println(strIn + "共" + (ch.length - 1) + "个字符");}}【程序39】题目:编写一个函数,输入n为偶数时,调用函数求1/2+1/4+...+1/n,当输入n为奇数时,调用函数1/1+1/3+...+1/n(利用指针函数)import java.util.Scanner;public class Prog39 {public static void main(String[] args) {System.out.print("请输入一个整数:");Scanner scan = new Scanner(System.in);int n = scan.nextInt();scan.close();if (n % 2 == 0)System.out.println("结果:" + even(n));elseSystem.out.println("结果:" + odd(n));}//奇数static double odd(int n) {double sum = 0;for (int i = 1; i < n + 1; i += 2) {sum += 1.0 / i;}return sum;}//偶数static double even(int n) {double sum = 0;for (int i = 2; i < n + 1; i += 2) {sum += 1.0 / i;}return sum;}}【程序40】题目:字符串排序。public class Prog40 {public static void main(String[] args) {String[] str = {"abc", "cad", "m", "fa", "f"};for (int i = str.length - 1; i >= 1; i--) {for (int j = 0; j <= i - 1; j++) {if (str[j].compareTo(str[j + 1]) < 0) {String temp = str[j];str[j] = str[j + 1];str[j + 1] = temp;}}}for (String subStr : str)System.out.print(subStr + " ");}}【程序41】题目:海滩上有一堆桃子,五只猴子来分。第一只猴子把这堆桃子凭据分为五份,多了一个,这只猴子把多的一个扔入海中,拿走了一份。第二只猴子把剩下的桃子又平均分成五份,又多了一个,它同样把多的一个扔入海中,拿走了一份,第三、第四、第五只猴子都是这样做的,问海滩上原来最少有多少个桃子?public class Prog41 {public static void main(String[] args) {int n;n = fun(0);System.out.println("原来有" + n + "个桃子");}private static int fun(int i) {if (i == 5)return 1;elsereturn fun(i + 1) * 5 + 1;}}【程序42】题目:809*??=800*??+9*??+1其中??代表的两位数,8*??的结果为两位数,9*??的结果为3位数。求??代表的两位数,及809*??后的结果。public class Prog42 {public static void main(String[] args) {int n = 0;boolean flag = false;for (int i = 10; i < 100; i++)if (809 * i == 800 * i + 9 * i + 1) {flag = true;n = i;break;}if (flag)System.out.println(n);elseSystem.out.println("无符合要求的数!");}}【程序43】题目:求0—7所能组成的奇数个数。public class Prog43 {public static void main(String[] args) {int count = 0;//声明由数字组成的数int n = 8;//一位数count = n / 2;//两位数count += (n - 1) * n / 2;//三位数count += (n - 1) * n * n / 2;//四位数count += (n - 1) * n * n * n / 2;//五位数count += (n - 1) * n * n * n * n / 2;//六位数count += (n - 1) * n * n * n * n * n / 2;//七位数count += (n - 1) * n * n * n * n * n * n / 2;System.out.println("0-7所能组成的奇数个数:" + count);}}【程序44】题目:一个偶数总能表示为两个素数之和。import java.util.Scanner;public class Prog44 {public static void main(String[] args) {System.out.print("请输入一个偶数:");Scanner scan = new Scanner(System.in);int n = scan.nextInt();scan.close();if (n % 2 != 0) {System.out.println("您输入的不是偶数!");return;}twoAdd(n);}//偶数分解为素数之和private static void twoAdd(int n) {for (int i = 2; i < n / 2 + 1; i++) {if (isPrime(i) && isPrime(n - i)) {System.out.println(n + "=" + (i) + "+" + (n - i));break;}}}//判断素数private static boolean isPrime(int m) {boolean flag = true;for (int i = 2; i < Math.sqrt(m) + 1; i++) {if (m % i == 0) {flag = false;break;}}return flag;}}【程序45】题目:判断一个素数能被几个9整除import java.util.Scanner;public class Prog45 {public static void main(String[] args) {System.out.print("请输入一个数:");Scanner scan = new Scanner(System.in);long l = scan.nextLong();long n = l;scan.close();int count = 0;while (n > 8) {n /= 9;count++;}System.out.println(l + "能被" + count + "个9整除。");}}【程序46】题目:两个字符串连接程序public class Prog46 {public static void main(String[] args) {String str1 = "lao lee";String str2 = "牛刀";String str = str1 + str2;System.out.println(str);}} 【程序47】题目:读取7个数(1—50)的整数值,每读取一个值,程序打印出该值个数的*。import java.util.Scanner;public class Prog47 {public static void main(String[] args) {System.out.print("请输入7个整数(1-50):");Scanner scan = new Scanner(System.in);int n1 = scan.nextInt();int n2 = scan.nextInt();int n3 = scan.nextInt();int n4 = scan.nextInt();int n5 = scan.nextInt();int n6 = scan.nextInt();int n7 = scan.nextInt();scan.close();printStar(n1);printStar(n2);printStar(n3);printStar(n4);printStar(n5);printStar(n6);printStar(n7);}static void printStar(int m) {System.out.println(m);for (int i = 0; i < m; i++)System.out.print("*");System.out.println();}}【程序48】题目:某个公司采用公用电话传递数据,数据是四位的整数,在传递过程中是加密的,加密规则如下:每位数字都加上5,然后用和除以10的余数代替该数字,再将第一位和第四位交换,第二位和第三位交换。public class Prog48 {public static void main(String[] args) {int n = 1234;int[] a = new int[4];for (int i = 3; i >= 0; i--) {a[i] = n % 10;n /= 10;}for (int i = 0; i < 4; i++)System.out.print(a[i]);System.out.println();for (int i = 0; i < a.length; i++) {a[i] += 5;a[i] %= 10;}int temp1 = a[0];a[0] = a[3];a[3] = temp1;int temp2 = a[1];a[1] = a[2];a[2] = temp2;for (int i = 0; i < a.length; i++)System.out.print(a[i]);}}【程序49】题目:计算字符串中子串出现的次数public class Prog49 {public static void main(String[] args) {String str = "I come from County DingYuan Province AnHui.";char[] ch = str.toCharArray();int count = 0;for (int i = 0; i < ch.length; i++) {if (ch[i] == ' ')count++;}count++;System.out.println("共有" + count + "个字串");}}【程序50】题目:有五个学生,每个学生有3门课的成绩,从键盘输入以上数据(包括学生号,姓名,三门课成绩),计算出平均成绩,将原有的数据和计算出的平均分数存放在磁盘文件"stud"中。import java.io.*;public class Prog50 {//定义学生模型String[] number = new String[5];String[] name = new String[5];float[][] grade = new float[5][3];float[] sum = new float[5];public static void main(String[] args) throws Exception {Prog50 stud = new Prog50();stud.input();stud.output();}//输入学号、姓名、成绩void input() throws IOException {BufferedReader br = new BufferedReader(new InputStreamReader(System.in));//录入状态标识boolean isRecord = true;while (isRecord) {try {for (int i = 0; i < 5; i++) {System.out.print("请输入学号:");number[i] = br.readLine();System.out.print("请输入姓名:");name[i] = br.readLine();for (int j = 0; j < 3; j++) {System.out.print("请输入第" + (j + 1) + "门课成绩:");grade[i][j] = Integer.parseInt(br.readLine());}System.out.println();sum[i] = grade[i][0] + grade[i][1] + grade[i][2];}isRecord = false;} catch (NumberFormatException e) {System.out.println("请输入一个数字!");}}}//输出文件void output() throws IOException {FileWriter fw = new FileWriter("E://java50//stud.txt");BufferedWriter bw = new BufferedWriter(fw);bw.write("No. " + "Name " + "grade1 " + "grade2 " + "grade3 " + "average");bw.newLine();for (int i = 0; i < 5; i++) {bw.write(number[i]);bw.write(" " + name[i]);for (int j = 0; j < 3; j++)bw.write(" " + grade[i][j]);bw.write(" " + (sum[i] / 5));bw.newLine();}bw.close();}}