LeetCode225——Implement Stack using Queues

标签：c++   leetcode   

Implement the following operations of a stack using queues.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• empty() -- Return whether the stack is empty.

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

Update (2015-06-11):

The class name of the Java function had been updated to MyStack instead of Stack.

实现：
class Stack {
public:
    // Push element x onto stack.
    void push(int x) {
        dq.push_back(x);
        last = x;
    }


    // Removes the element on top of the stack.
    void pop() {
        if (empty()) return;
        vector<int> vec;
        while (!empty()) {
            vec.push_back(dq.front());
            dq.pop_front();
        }
        for (int i = 0; i < vec.size()-1; i++) {
            push(vec[i]);
        }
    }


    // Get the top element.
    int top() {
        return last;
    }


    // Return whether the stack is empty.
    bool empty() {
        return dq.size() == 0;
    }
private:
    deque<int> dq;
    int last;
};

LeetCode225——Implement Stack using Queues

标签：c++   leetcode   

原文地址：http://blog.csdn.net/booirror/article/details/47173083