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 1:
输入:
["CQueue","appendTail","deleteHead","deleteHead","deleteHead"]
[[],[3],[],[],[]]
输出:[null,null,3,-1,-1]
示例 2:
输入:
["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
[[],[],[5],[2],[],[]]
输出:[null,-1,null,null,5,2]
提示:
1 <= values <= 10000
最多会对 appendTail、deleteHead 进行 10000 次调用
class CQueue {
Stack<Integer> A;
Stack<Integer> B;
public CQueue() {
A = new Stack<Integer>();
B = new Stack<Integer>();
}
public void appendTail(int value) {
A.push(value);
}
public int deleteHead() {
while(!A.empty()){
B.push(A.pop());
}
int result = B.empty() ? -1 : B.pop();
while(!B.empty()){
A.push(B.pop());
}
return result;
}
}