剑指 Offer 09. 用两个栈实现队列

题解

class CQueue {
    Stack<Integer> a, b;
    
    public CQueue() {
        a = new Stack<Integer>(); 
        b = new Stack<Integer>();
    }
    
    public void appendTail(int value) {
        a.push(value);//新加的值直接加在a中就可以了
    }
    
    public int deleteHead() {
        if(b.empty()){//在进行删除的时候先判定b中是否有数据，如果没有就从a中拿数据
            while(!a.empty()){
                b.push(a.pop());
            }
        }

        //最后再进行判定就可以了
        if(!b.empty()){
            return b.pop();
        }

        return -1;
    }
}

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