100. Implement Queue using Stacks

-232. Implement Queue using Stacks My Submissions QuestionEditorial Solution

Total Accepted: 44621 Total Submissions: 130935 Difficulty: Easy

Implement the following operations of a queue using stacks.

push(x) – Push element x to the back of queue.

pop() – Removes the element from in front of queue.

peek() – Get the front element.

empty() – Return whether the queue is empty.

Notes:

You must use only standard operations of a stack – which means only push to top, peek/pop from top, size, and is empty operations are valid.

Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.

You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

用栈实现队列：

老题-简单：自己看着实现

class Queue {
public:
stack<int> s1,s2;
// Push element x to the back of queue.
void push(int x) {
s1.push(x);
}

// Removes the element from in front of queue.
void pop(void) {
if(!s2.empty()){
s2.pop();
}
else{
while(!s1.empty()){
s2.push(s1.top());
s1.pop();
}
if(!s2.empty())s2.pop();
}
}

// Get the front element.
int peek(void) {
if(!s2.empty())return s2.top();
else{
while(!s1.empty()){
s2.push(s1.top());
s1.pop();
}
return s2.top();
}
}

// Return whether the queue is empty.
bool empty(void) {
return s1.empty()&&s2.empty();
}
};