PROBLEM

剑指 Offer 09. 用两个栈实现队列

难度 简单

MY ANSWER

栈in负责append，栈out负责delete。append时直接push进in就好，delete时先检查out是否为空，out空的话再检查in是否为空，in也空的话返回-1，否则将in里的一个个出栈并压到out里，最后弹出一个。若out非空，则直接弹出一个。

class CQueue {
public:
    stack<int> in;
    stack<int> out;
    CQueue() {}
    
    void appendTail(int value) {
        in.push(value);
    }
    
    int deleteHead() {
        if(!out.empty()) {
           int tmp = out.top();
           out.pop();
           return tmp; 
        }
        else {
            if(in.empty()) {
                return -1;
            }
            else {
                while(!in.empty()) {
                    out.push(in.top());
                    in.pop();
                }
                int tmp = out.top();
                out.pop();
                return tmp; 
            }
        }
    }
};

/**
 * Your CQueue object will be instantiated and called as such:
 * CQueue* obj = new CQueue();
 * obj->appendTail(value);
 * int param_2 = obj->deleteHead();
 */

/**
 * Your CQueue object will be instantiated and called as such:
 * CQueue* obj = new CQueue();
 * obj->appendTail(value);
 * int param_2 = obj->deleteHead();
 */

BETTER SOLUTION

一样。

SUMMARY

学习用两个栈实现队列。