[洛谷] 刷题栈队列

1.后缀表达式

2.表达式括号匹配

3.表达式求值

4.表达式的转换

5.机器翻译

1.后缀表达式

后缀表达式 - 洛谷

#include<iostream>
#include<cstdio>
using namespace std;int stk[100]; // 用于存储操作数的栈
int index = 0; // 栈顶索引int main() {char op; // 当前读取的字符int now = 0; // 当前构建的数字bool readingNumber = false; // 是否正在读取一个数字while ((op = getchar()) != '@') { // 读取字符直到结束符 '@'if (op >= '0' && op <= '9') {// 构建当前数字now *= 10;now += op - '0';readingNumber = true;}else if (op == '.') {// 数字结束，压入栈中if (readingNumber) {stk[++index] = now;now = 0;readingNumber = false;}}else if (op == '+') {// 加法操作stk[index - 1] = stk[index - 1] + stk[index];index--;}else if (op == '-') {// 减法操作stk[index - 1] = stk[index - 1] - stk[index];index--;}else if (op == '*') {// 乘法操作stk[index - 1] = stk[index - 1] * stk[index];index--;}else if (op == '/') {// 除法操作，结果向零取整stk[index - 1] = stk[index - 1] / stk[index];index--;}}// 输出最终结果cout << stk[1] << endl;return 0;
}

2.表达式括号匹配

表达式括号匹配 - 洛谷

#include<iostream>
#include<bits/stdc++.h>
using namespace std;int main()
{string s;cin >> s;int isMatch = 0;for (int i = 0; i < s.length(); i++) {if (s[i] == '(') {isMatch++;}else if (s[i] == ')') {isMatch--;if (isMatch < 0) {cout << "NO";return 0;}}}if (!isMatch) {cout << "YES";}else {cout << "NO";}return 0;}

3.表达式求值

[NOIP2013 普及组] 表达式求值 - 洛谷

如果用Python

print(intput()%10000)

首先是思路：

可以用一个栈储存运算符
并用另一个栈储存需要运算的数字

#include <iostream>
#include <stack>
#include <string>using namespace std;stack<int> num; // 定义一个栈存储数字
stack<char> op; // 定义一个栈存储运算符
string input;
int sum = 0, ans, t, t1, t2; // t, t1, t2均为临时变量int applyOp(int a, int b, char oper) {if (oper == '*') return (a * b) % 10000;if (oper == '+') return (a + b) % 10000;return 0;
}int main() {cin >> input;for (int i = 0; i < input.length(); i++) {if (isdigit(input[i])) { // 字符转数字sum = sum * 10 + (input[i] - '0');if (i == input.length() - 1 || !isdigit(input[i + 1])) {sum = sum % 10000; // 取模，后四位num.push(sum);sum = 0;}}else if (input[i] == '+' || input[i] == '*') { // 运算符while (!op.empty() && (op.top() == '*' || (op.top() == '+' && input[i] == '+'))) {t1 = num.top(); num.pop();t2 = num.top(); num.pop();t = applyOp(t2, t1, op.top());op.pop();num.push(t);}op.push(input[i]);}}while (!op.empty()) {t1 = num.top(); num.pop();t2 = num.top(); num.pop();t = applyOp(t2, t1, op.top());op.pop();num.push(t);}ans = num.top(); // 可直接输出栈顶元素cout << ans << endl;return 0;
}

4.表达式的转换

表达式的转换 - 洛谷

#include <bits/stdc++.h>
using namespace std;
stack<char> dat, op;
stack<int> num, dat2;
int check(char c)
{switch (c){case '+':return 1;case '-':return 1;case '*':return 2;case '/':return 2;case '^':return 3;case '(':return 0;case ')':return 0;default:return -1;}
}
int js(int x, int y, char t)
{switch (t){case '+':return x + y;case '-':return x - y;case '*':return x * y;case '/':return x / y;case '^':return pow(x, y);default:return -0x3f3f3f3f;}
}
void change(string s)
{int len = s.size();for (int i = 0; i < len; i++){if (isdigit(s[i]))dat.push(s[i]);else if (s[i] == '(')op.push(s[i]);else if (s[i] == ')'){char t = op.top();while (t != '('){op.pop();dat.push(t);t = op.top();}op.pop();//要弹出左括号}else if (check(s[i]) >= 1 && check(s[i]) <= 3)//为运算符{if (!op.empty()){char t = op.top();while (!op.empty() && check(s[i]) <= check(t)){if (check(s[i]) == check(t) && s[i] == '^')break;//在s[i]与栈顶都是^号时也能进栈op.pop();dat.push(t);if (!op.empty())t = op.top();}}op.push(s[i]);}}while (!op.empty()){char t = op.top();op.pop();dat.push(t);}while (!dat.empty()){char t = dat.top();dat.pop();op.push(t);}while (!op.empty()){char t = op.top();cout << t << ' ';op.pop();dat.push(t);}cout << endl;
}
void calc()
{while (!dat.empty()){char t = dat.top();dat.pop();op.push(t);}while (!op.empty()){char t = op.top();op.pop();if (isdigit(t))num.push(t - '0');else{int x = num.top();num.pop();int y = num.top();num.pop();num.push(js(y, x, t));//传参数时要把x和y反过来while (!num.empty()){int t = num.top();num.pop();dat2.push(t);}while (!dat2.empty()){int t = dat2.top();cout << t << ' ';dat2.pop();num.push(t);}while (!op.empty()){char t = op.top();cout << t << ' ';op.pop();dat.push(t);}while (!dat.empty()){char t = dat.top();dat.pop();op.push(t);}cout << endl;}}
}
int main()
{string s;cin >> s;change(s);calc();return 0;
}

5.机器翻译

https://www.luogu.com.cn/problem/P1540

import java.util.*;/*** Author : yjy* Desc*/
public class Main {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int N = sc.nextInt();int M = sc.nextInt();int[] arr = new int[M];for(int i=0;i<M;i++){arr[i] = sc.nextInt();}int res = 0;Queue<Integer> queue = new LinkedList<>();for (int i = 0; i < M; i++) {if(queue.contains(arr[i])){continue;}else{if(queue.size()==N){queue.poll();}queue.offer(arr[i]);res++;}}System.out.println(res);}
}

#include<iostream>
#include<stdio.h>
#include<algorithm>
using namespace std;
int n, m, x, ans, l, r, a[1005], b[1005];
int main()
{cin >> m >> n;l = 0, r = 0;//初始化两个指针for (int i = 1; i <= n; i++) {scanf("%d", &x);//边读边做if (a[x] == 0) {//没有被访问过ans++;r++;b[r] = x; a[x] = 1;if (r > m) {l++; a[b[l]] = 0;}}}cout << ans;return 0;
}