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用栈实现队列

程序员文章站 2024-01-28 21:52:46
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用栈实现队列

利用一个临时栈,调换顺序

class MyQueue {
public:
    /** Initialize your data structure here. */
    MyQueue() {
        
    }
    
    /** Push element x to the back of queue. */
    void push(int x) {
        stack<int> tmp_stack;
        while(!data_stack.empty())
        {
            tmp_stack.push(data_stack.top());
            data_stack.pop();
        }
        tmp_stack.push(x);
        while(!tmp_stack.empty())
        {
            data_stack.push(tmp_stack.top());
            tmp_stack.pop();
        }
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        int x = data_stack.top();
        data_stack.pop();
        return x;
    }
    
    /** Get the front element. */
    int peek() {
        return data_stack.top();
    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
        return data_stack.empty();
    }

private:
    stack<int> data_stack;
};

/**
 * 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();
 */

2:

class MyQueue {
public:
    /** Initialize your data structure here. */
    MyQueue() {
        
    }
    //双栈法,一个用来存输入,一个用来存输出,当需要输出时,如果output为空,就把input的部分放进来,相当于就调换了顺序
    //如果不为空,就可以直接out.pop(),因为放在output的是已经调换过的了
    /** Push element x to the back of queue. */
    void push(int x) {
        input.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        adjust();
        int x = output.top();
        output.pop();
        return x;
    }
    
    /** Get the front element. */
    int peek() {
        adjust();
        return output.top();
    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
        return input.empty()&&output.empty();
    }
    


private:
    stack<int> input;
    stack<int> output;
    
    void adjust()
    {
        if(!output.empty())
            return;
        while(!input.empty())
        {
            output.push(input.top());
            input.pop();
        }
    }
};

/**
 * 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();
 */