题目描述
使用栈实现队列的下列操作:
push(x) – 将一个元素放入队列的尾部。
pop() – 从队列首部移除元素。
peek() – 返回队列首部的元素。
empty() – 返回队列是否为空。
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
C++ 代码
class MyQueue {
public:
/** Initialize your data structure here. */
MyQueue() {
}
/** Push element x to the back of queue. */
void push(int x) {
s1.push(x);
}
/** Removes the element from in front of queue and returns that element. */
int pop() {
while(!s1.empty())
{
s2.push(s1.top());
s1.pop();
}
int r = s2.top();
s2.pop();
while(!s2.empty())
{
s1.push(s2.top());
s2.pop();
}
return r;
}
/** Get the front element. */
int peek() {
while(!s1.empty())
{
s2.push(s1.top());
s1.pop();
}
int r = s2.top();
while(!s2.empty())
{
s1.push(s2.top());
s2.pop();
}
return r;
}
/** Returns whether the queue is empty. */
bool empty() {
return s1.empty();
}
private:
stack<int> s1;
stack<int> s2;
};
/**
* 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();
* bool param_4 = obj->empty();
*/