代码随想录第二十七天

字符串-用栈实现队列

题目链接

class MyQueue {
public:
    stack<int> stIn;
    stack<int> stOut;
    MyQueue() {

    }
    
    void push(int x) {
        stIn.push(x);
    }
    
    int pop() {
        if(stOut.empty()){
            while(!stIn.empty()){
                stOut.push(stIn.top());
                stIn.pop();
            }
        }
        int result = stOut.top();
        stOut.pop();
        return result;

    }
    
    int peek() {
        int result = this->pop();//直接复用前面的pop函数，记得pop后要保存
        stOut.push(result);
        return result;
    }
    
    bool empty() {
        return stOut.empty() && stIn.empty();
    }
};

/**
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue* obj = new MyQueue();
 * obj->push(x);
 * int param_2 = obj->pop();
 * int param_3 = obj->peek();
 * bool param_4 = obj->empty();
 */

typedef struct {
    int stInTop, stOutTop;
    int stIn[100],stOut[100];
} MyQueue;


MyQueue* myQueueCreate() {
    MyQueue* queue = (MyQueue*)malloc(sizeof(MyQueue));
    queue->stInTop = 0;
    queue->stOutTop = 0;
    return queue;
}

void myQueuePush(MyQueue* obj, int x) {
    obj->stIn[(obj->stInTop)++] = x;
}

int myQueuePop(MyQueue* obj) {
    int stInTop = obj->stInTop;
    int stOutTop = obj->stOutTop;
    if(stOutTop == 0){
        while(stInTop > 0)obj->stOut[stOutTop++] = obj->stIn[stInTop];
    }

    int top = obj->stOut[--stOutTop];

    while(stOutTop > 0)obj->stIn[stInTop++] = obj->stOut[--stOutTop];

    obj->stInTop = stInTop;
    obj->stOutTop = stOutTop;

    return top;

}

int myQueuePeek(MyQueue* obj) {
    return obj->stIn[0];
}

bool myQueueEmpty(MyQueue* obj) {
    return obj->stInTop == 0 && obj->stOutTop == 0;
}

void myQueueFree(MyQueue* obj) {
    obj->stInTop = 0;
    obj->stOutTop = 0;
}

/**
 * Your MyQueue struct will be instantiated and called as such:
 * MyQueue* obj = myQueueCreate();
 * myQueuePush(obj, x);
 
 * int param_2 = myQueuePop(obj);
 
 * int param_3 = myQueuePeek(obj);
 
 * bool param_4 = myQueueEmpty(obj);
 
 * myQueueFree(obj);
*/