剑指 Offer 09. 用两个栈实现队列 #

题目 #

用两个栈实现一个队列。
队列的声明如下，请实现它的两个函数 appendTail 和 deleteHead ，分别完成在队列尾部插入整数和在队列头部删除整数的功能。
(若队列中没有元素，deleteHead 操作返回 -1 )

思路 #

代码 #

class CQueue {
    Stack<Integer> inStack, outStack;

    public CQueue() {
        this.inStack = new Stack<>();
        this.outStack = new Stack<>();
    }
    
    public void appendTail(int value) {
        this.inStack.push(value);
    }
    
    public int deleteHead() {
        if (this.outStack.size() == 0 && this.inStack.size() == 0) return -1;
        if (this.outStack.size() == 0) {
            while (this.inStack.size() != 0) {
                this.outStack.push(this.inStack.pop());
            }
        }
        return this.outStack.pop();
    }
}

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