两个栈实现一个队列

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九度OJ1512 http://ac.jobdu.com/problem.php?pid=1512
剑指offer面试题7

思路分析

两个队列，一个“入栈”inStack，当有数据进入队列时，只往inStack里压栈；一个“出栈”outStack，当有数据出队列时，只能从outStack中出。

代码实现

使用c++实现

#include<cstdio>#include<stack>#include<cstring>using namespace std;class MyQueue {public:    void PUSH(int);    void POP();private:    stack<int> inStack;    stack<int> outStack;};void MyQueue::PUSH(int val) {    inStack.push(val);}void MyQueue::POP(void) {    if (outStack.empty()) {        if (inStack.empty()) {            printf("-1\n");            return;        } else {            while (!inStack.empty()) {                outStack.push(inStack.top());                inStack.pop();            }        }    }    printf("%d\n", outStack.top());    outStack.pop();}int main() {    int n;    MyQueue que;    scanf("%d", &n);    for (int i = 0; i != n; ++i) {        char MyOrder[5]; //只需5个空间即可（"PUSH"4个字符加上末尾的'\0'）        scanf("%s", MyOrder);        if (strcmp("PUSH", MyOrder) == 0) {            int val;            scanf("%d", &val);            que.PUSH(val);        }        else if (strcmp("POP", MyOrder) == 0) {            que.POP();        }        else {            return 0;        }    }    return 0;}/**************************************************************    Problem: 1512    User: buptxxz    Language: C++    Result: Accepted    Time:70 ms    Memory:1184 kb****************************************************************/

使用java实现

import java.util.Scanner;import java.util.Stack;public class Main {    Stack<Integer> inStack = new Stack<Integer>();    Stack<Integer> outStack = new Stack<Integer>();    public void push(int e) {        inStack.push(e);    }    public void pop() {        if (inStack.empty() && outStack.empty()) {            System.out.println(-1);        } else if (outStack.empty()) {            while (!inStack.empty()) {                outStack.push(inStack.pop());            }            System.out.println(outStack.pop());        } else {            System.out.println(outStack.pop());        }    }    public static void main(String[] args) {        Main M = new Main();        Scanner cin = new Scanner(System.in);        String kaseNum = cin.nextLine();        int kase = Integer.parseInt(kaseNum);        for (int i = 0; i < kase; ++i) {            String cmd = cin.next();            if ("PUSH".equals(cmd)) {                int elem = Integer.parseInt(cin.next());                M.push(elem);            } else {                M.pop();            }        }        cin.close();    } // main} // class/**************************************************************    Problem: 1512    User: buptxxz    Language: Java    Result: Accepted    Time:2150 ms    Memory:104104 kb****************************************************************/

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