【LeetCode】面试题09. 用两个栈实现队列

题目:

思路:

栈先进后出，队列先进先出性质。

代码:

Python

class CQueue(object):

    def __init__(self):
        self.in_stack = []
        self.out_stack = []


    def appendTail(self, value):
        """
        :type value: int
        :rtype: None
        """
        self.in_stack.append(value)


    def deleteHead(self):
        """
        :rtype: int
        """
        if self.out_stack:
            return self.out_stack.pop()
        if not self.in_stack:
            return -1
        while self.in_stack:
            self.out_stack.append(self.in_stack.pop())
        return self.out_stack.pop()

C++

class CQueue {
    stack<int> inStack;
    stack<int> outStack; 
public:
    CQueue() {

    }
    
    void appendTail(int value) {
        inStack.push(value);
    }
    
    int deleteHead() {
        if (!outStack.empty()) {
            int tmp = outStack.top();
            outStack.pop();
            return tmp;
        }
        if (inStack.empty()) {
            return -1;
        }
        int tmp;
        while(!inStack.empty()) {
            tmp = inStack.top();
            inStack.pop();
            outStack.push(tmp);
        }
        outStack.pop();
        return tmp;
    }
};