LeetCode:Implement Queue using Stacks

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).

两个栈实现队列。

class Queue {
private:
stack<int> stack1,stack2;
public:
// Push element x to the back of queue.
void push(int x) {

stack1.push(x);

}

// Removes the element from in front of queue.
void pop(void) {
if(stack2.empty())
{
while(!stack1.empty())
{
stack2.push(stack1.top());
stack1.pop();
}
}
stack2.pop();

}

// Get the front element.
int peek(void) {
if(stack2.empty())
{
while(!stack1.empty())
{
stack2.push(stack1.top());
stack1.pop();
}
}
return stack2.top();

}

// Return whether the queue is empty.
bool empty(void) {
if(stack1.empty()&&stack2.empty())
return true;
else
return false;

}
};