LeetCode 232. Implement Queue using Stacks--用2個棧來實現一個隊列--C++解法

LeetCode 232. Implement Queue using Stacks–C++解法

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LeetCode題解專欄：LeetCode題解
我做的所有的LeetCode的題目都放在這個專欄裏，大部分題目Java和Python的解法都有。

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題目地址：Implement Queue using Stacks - LeetCode

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Implement the following operations of a queue using stacks.

push(x) – Push element x to the back of queue.
pop() – Removes the element from in front of queue.
peek() – Get the front element.
empty() – Return whether the queue is empty.
Example:

MyQueue queue = new MyQueue();

queue.push(1);
queue.push(2);  
queue.peek();  // returns 1
queue.pop();   // returns 1
queue.empty(); // returns false

Notes:

You must use only standard operations of a stack – which means only push to top, peek/pop from top, size, and is empty operations are valid.
Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

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這道題目是經典的用2個棧來實現一個隊列，達到入隊和出隊的時間複雜度都是O(1)。

C++解法如下：

class MyQueue {
public:
    stack<int> inbox, outbox;

    /** Initialize your data structure here. */
    MyQueue() {
        ;
    }

    /** Push element x to the back of queue. */
    void push(int x) {
        inbox.push(x);
    }

    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        int temp = peek();
        outbox.pop();
        return temp;
    }

    /** Get the front element. */
    int peek() {
        cout << outbox.empty() << endl;
        if (outbox.empty() == 1) {
            while (inbox.empty() == 0) {
                outbox.push(inbox.top());
                inbox.pop();
            }
        }
        return outbox.top();
    }

    /** Returns whether the queue is empty. */
    bool empty() {
        return inbox.empty() && outbox.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();
 */