2022-4-24
剑指 Offer 09. 用两个栈实现队列
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 )
示例一：
输入：
["CQueue","appendTail","deleteHead","deleteHead"]
[[],[3],[],[]]
输出：
[null,null,3,-1]
示例二：
输入：
["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
[[],[],[5],[2],[],[]]
输出：
[null,-1,null,null,5,2]
解答：
class CQueue {
private Stack<Integer> stack1;
private Stack<Integer> stack2;
public CQueue() {
//建栈 一个为进入栈另一个为取出栈
stack1 = new Stack<>();
stack2 = new Stack<>();
}
public void appendTail(int value) {
stack1.push(value);
}
public int deleteHead() {
//当取出栈不为空，则取出
if (!stack2.isEmpty()){
return stack2.pop();
}
//当取出栈为空 把进入栈的数据全部放入取出栈 然后取出
else{
while (!stack1.isEmpty()){
stack2.push(stack1.pop());
}
return stack2.isEmpty() ? -1:stack2.pop();
}
}
}
/**
* Your CQueue object will be instantiated and called as such:
* CQueue obj = new CQueue();
* obj.appendTail(value);
* int param_2 = obj.deleteHead();
*/
