剑指 Offer 09. 用两个栈实现队列

思路#

代码实现#

class CQueue {
private:
    stack<int> s1;  //用于插入
    stack<int> s2;  //用于删除
public:
    CQueue() {
        
    }
    
    void appendTail(int value) {
        s1.push(value);
    }
    
    int deleteHead() {
        if(s2.empty()) {
            if(s1.empty()) {
                return -1;
            } else {
                while(!s1.empty()) {
                    s2.push(s1.top());
                    s1.pop();
                }
                
                int x = s2.top();
                s2.pop();
                return x;
            }
        } else {
            int x = s2.top();
            s2.pop();
            return x;
        }
    }
};

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

复杂度分析#

 

参考#

用两个栈实现队列-LeetCode官方

面试题09. 用两个栈实现队列（清晰图解）