栈实现队列
请你仅使用两个栈实现先入先出队列。队列应当支持一般队列支持的所有操作(push
、pop
、peek
、empty
):
实现 MyQueue
类:
void push(int x)
将元素 x 推到队列的末尾int pop()
从队列的开头移除并返回元素int peek()
返回队列开头的元素boolean empty()
如果队列为空,返回true
;否则,返回false
java
class MyQueue {
Stack<Integer> stack = new Stack<>();
Stack<Integer> tmp = new Stack<>();
public MyQueue() {
}
public void push(int x) {
stack.push(x);
}
public int pop() {
tmp.empty();
while(!stack.empty()){
tmp.push(stack.peek());
stack.pop();
}
Integer res = tmp.pop();
while(!tmp.empty()){
stack.push(tmp.peek());
tmp.pop();
}
return res;
}
public int peek() {
tmp.empty();
while(!stack.empty()){
tmp.push(stack.peek());
stack.pop();
}
Integer res = tmp.peek();
while(!tmp.empty()){
stack.push(tmp.peek());
tmp.pop();
}
return res;
}
public boolean empty() {
return stack.empty();
}
}
用另一个栈实现