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实现一个MyQueue类,该类用两个栈来实现一个队列。
示例:
MyQueue queue = new MyQueue();
queue.push(1);
queue.push(2);
queue.peek(); // 返回 1
queue.pop(); // 返回 1
queue.empty(); // 返回 false
说明:
push to top
, peek/pop from top
, size
和 is empty
操作是合法的。class MyQueue:
def __init__(self):
"""
Initialize your data structure here.
"""
self._s1, self._s2 = [], []
def push(self, x: int) -> None:
"""
Push element x to the back of queue.
"""
self._s1.append(x)
def pop(self) -> int:
"""
Removes the element from in front of queue and returns that element.
"""
if len(self._s2) == 0:
while self._s1:
self._s2.append(self._s1.pop())
return self._s2.pop()
def peek(self) -> int:
"""
Get the front element.
"""
if len(self._s2) == 0:
while self._s1:
self._s2.append(self._s1.pop())
return self._s2[-1]
def empty(self) -> bool:
"""
Returns whether the queue is empty.
"""
return len(self._s1) + len(self._s2) == 0
# Your MyQueue object will be instantiated and called as such:
# obj = MyQueue()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.peek()
# param_4 = obj.empty()
class MyQueue {
private Stack<Integer> s1;
private Stack<Integer> s2;
/** Initialize your data structure here. */
public MyQueue() {
s1 = new Stack<>();
s2 = new Stack<>();
}
/** Push element x to the back of queue. */
public void push(int x) {
s1.push(x);
}
/** Removes the element from in front of queue and returns that element. */
public int pop() {
if (s2.empty()) {
while (!s1.empty()) {
s2.push(s1.pop());
}
}
return s2.pop();
}
/** Get the front element. */
public int peek() {
if (s2.empty()) {
while (!s1.empty()) {
s2.push(s1.pop());
}
}
return s2.peek();
}
/** Returns whether the queue is empty. */
public boolean empty() {
return s1.empty() && s2.empty();
}
}
/**
* Your MyQueue object will be instantiated and called as such:
* MyQueue obj = new MyQueue();
* obj.push(x);
* int param_2 = obj.pop();
* int param_3 = obj.peek();
* boolean param_4 = obj.empty();
*/
type MyQueue struct {
s1, s2 []int
}
/** Initialize your data structure here. */
func Constructor() MyQueue {
return MyQueue{
s1: make([]int, 0),
s2: make([]int, 0),
}
}
/** Push element x to the back of queue. */
func (this *MyQueue) Push(x int) {
this.s1 = append(this.s1, x)
}
/** Removes the element from in front of queue and returns that element. */
func (this *MyQueue) Pop() int {
if len(this.s2) == 0 {
this.transfer()
}
v := this.s2[len(this.s2)-1]
this.s2 = this.s2[:len(this.s2)-1]
return v
}
/** Get the front element. */
func (this *MyQueue) Peek() int {
if len(this.s2) == 0 {
this.transfer()
}
return this.s2[len(this.s2)-1]
}
/** Returns whether the queue is empty. */
func (this *MyQueue) Empty() bool {
return len(this.s1) == 0 && len(this.s2) == 0
}
func (this *MyQueue) transfer() {
for len(this.s1) > 0 {
this.s2 = append(this.s2, this.s1[len(this.s1)-1])
this.s1 = this.s1[:len(this.s1)-1]
}
}
/**
* Your MyQueue object will be instantiated and called as such:
* obj := Constructor();
* obj.Push(x);
* param_2 := obj.Pop();
* param_3 := obj.Peek();
* param_4 := obj.Empty();
*/
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