c语言常见上机题

快速排序

快排很容易进入无限递归，写的时候要注意边界问题

#include<iostream>using namespace std;int n;const int N = 1e6 +10;void qsort(int a[],int l,int r){if(l>=r) return;int x=a[l],i=l-1,j=r+1;while(i<j){do i++;while(a[i]<x);do j--;while(a[j]>x);if(i<j) swap(a[i],a[j]);}qsort(a,l,j);qsort(a,j+1,r);
}int main(){scanf("%d",&n);int a[n];for(int i=0;i<n;i++){scanf("%d",&a[i]);}qsort(a,0,n-1);for(int i=0;i<n;i++){printf("%d ",a[i]);}return 0;}

求前n项分数和

#include<stdio.h>int main(){int n=10;double sum = 0.0;for (int i = 1; i <= n;i++){sum += 1.0 / i;}printf("f(%d)=%f\n", n, sum);return 0;
}
//变式
#include<stdio.h>int main(){int n=10000;double sum = 0.0;int sign = 1;for (int i = 1; i <= n;i++){sum += sign*1.0 / i;sign = -sign;}printf("f(%d)=%f\n", n, sum);return 0;
}

整数分解

#include<stdio.h>int main(){int x;scanf("%d", &x);x = 12345;do{int d = x % 10;printf("%d", d);if(x>=10){printf(" ");//在非最后一轮输出空格}x /= 10;} while (x > 0);return 0;
}

整数逆序

#include<stdio.h>int main(){int x;scanf("%d", &x);int t = 0;do{int d = x % 10;t = t * 10 + d;x /= 10;} while (x > 0);printf("t=%d\n", t);//   do{
//      int d = x % 10;
//      printf("%d", d);
//      if(x>=10){
//         printf(" ");//在非最后一轮输出空格
//      }
//      x /= 10;
//   } while (x > 0);return 0;
}

求最大公约数

#include<stdio.h>int main(){int a, b;int t;a = 12, b = 6;while (b!=0){t = a % b;a = b;b = t;printf("%d", a);}return 0;
}

全排列问题

#include <iostream>
#include <bits/stdc++.h>
using namespace std;
//记录路径
int path[100];
// 记录每一位是否访问
int status[100];
int n;
/*
u是递归层数，a[]是存放待排列数字的数组
*/
void dfs(int u, int a[])
{if (u == n){for (int i = 0; i < n; i++){//输出路径printf("%d ", path[i]);}puts(""); // 每个排列之间的换行return;}for (int i = 0; i < n; i++){if (!status[i]){path[u] = a[i];status[i] = true;dfs(u + 1, a);status[i] = false;//恢复现场，回溯}}}int main()
{//n是待排列数字的个数scanf("%d", &n);int a[n]; // 记录待排列数字// 输入待排列数字for (int i = 0; i < n; i++){cin >> a[i];}dfs(0, a);return 0;
}
//没有给定数组长度
#include <iostream>
#include <bits/stdc++.h>
using namespace std;
//记录路径
int path[100];
// 记录每一位是否访问
int status[100];
int n;
/*
u是递归层数，a[]是存放待排列数字的数组
*/
void dfs(int u, int a[])
{if (u == n){for (int i = 0; i < n; i++){//输出路径printf("%d ", path[i]);}puts(""); // 每个排列之间的换行return;}for (int i = 0; i < n; i++){if (!status[i]){path[u] = a[i];status[i] = true;dfs(u + 1, a);status[i] = false;//恢复现场，回溯}}}int main()
{//n是待排列数字的个数// scanf("%d", &n);int a[100]; // 记录待排列数字// 输入待排列数字int x;n=0;while (cin>>x,x){a[n++] = x;if(cin.get()=='\n') break;//回车结束循环}dfs(0, a);return 0;
}

选择排序

#include<iostream>using namespace std;const int N = 1010;
int a[N];
int n;void selectSort(){for (int i = 0; i < n;i++){int pos = i;for (int j = i + 1; j < n;j++){if(a[j]<a[pos])pos = j;}swap(a[i], a[pos]);}
}int main()
{cin >> n;for (int i = 0; i < n;i++){cin >> a[i];}selectSort();for (int i = 0; i < n;i++){cout << a[i] << " ";}return 0;
}

蜜蜂路线

#include <cstdio>
int main(){long long f[105];f[1]=1;f[2]=2;for(int i=3;i<=100;i++) f[i]=f[i-1]+f[i-2];int n;int a,b;scanf("%d%d",&a,&b);printf("%lld\n",f[b-a]);return 0;
}

读写文件

#include<stdio.h>
#include<stdlib.h>int cmp(const void *a, const void *b)
{const int *pa = a, *pb = b;return *pb - *pa; // 逆序比较
}
int main(){const char *filename = "original.txt";//打开文件读取数据//打开文件FILE *fin;if((fin=fopen(filename,"r"))==NULL){perror(filename);return 1;//读取文件失败}//读取数据int a[1024];int n = 0;while ((fscanf(fin,"%d",&a[n])==1)){n++;}//关闭文件fclose(fin);//数据排序qsort(a, n, sizeof(int), cmp);//写入文件//打开文件FILE *fout;if ((fout = fopen(filename, "w")) == NULL){perror(filename);return 2; // 写文件失败}//写入数据for (int i = 0; i < n; i++)fprintf(fout, "%d\n", a[i]);//关闭文件fclose(fout);return 0;
}

水仙花数

#include<iostream>
#include<cstring>
#include<algorithm>using namespace std;bool check(int x){int sum = 0, y = x;//用y暂存下x的取值while (x){int t = x % 10;//取个位x /= 10;//去除末位sum += t * t * t;}return sum == y;
}
int main(){int m, n;while (cin>>m>>n,m)//只要有m在输入，循环就会一直执行{int cnt = 0;for (int i = m;i<=n;i++){if(check(i)){cout << i << " ";cnt++;}}if (!cnt){cout << "no";}cout << endl;}return 0;
}

逆置链栈

#include<stdio.h>
#include<stdlib.h>typedef char ElementType;
typedef struct SNode *Stack;
struct SNode
{ElementType Data;struct SNode *Next;
};
//构建一个堆栈的头结点，返回指针
Stack Create()
{Stack s;s = (Stack)malloc(sizeof(struct SNode));s->Next = NULL;return s;
}
int IsEmpty(Stack s)
{return (s->Next == NULL);
}
void Push(ElementType item,Stack s)
{struct SNode *temp;temp = (Stack)malloc(sizeof(struct SNode));temp->Data = item;temp->Next = s->Next;s->Next = temp;
}
//删除并返回堆栈s的栈顶元素
ElementType Pop(Stack s)
{struct SNode *temp;ElementType topElem;if(IsEmpty(s)){printf("堆栈空");return NULL;}else{temp = s->Next;s->Next = temp->Next;topElem = temp->Data;free(temp);return topElem;}
}
void PrintStack(Stack s){if(s==NULL){printf("栈不存在\n");return;}//s = s->Next;while (!IsEmpty(s)){printf("%c", Pop(s));}printf("\n");
}
int main(){Stack s;s=Create();char c;int i=0; for(i=0;i<10;i++){scanf("%c",&c);Push(c,s);}PrintStack(s);return 0;
}

判断完数

#include<stdio.h>int main()
{int num, sum;for (num = 1; num <= 1000;num++){sum = 0;for (int i = 1; i <= num;i++){if(num%i==0){sum += i;}}if(sum==num){printf("%d",num);}}return 0;
}

冒泡排序

#include<iostream>using namespace std;int main(){int n;cin >> n;int a[n];for (int i = 0; i < n;i++){cin >> a[i];}for (int i = 0; i < n - 1;i++){for (int j = 0; j < n - i - 1; j++){if(a[j]>a[j+1])swap(a[j], a[j + 1]);}}for (int i = 0; i < n;i++){cout << a[i] << " ";}return 0;
}