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).

不难，想明白就好，貌似之前看到过这样的题目；一个栈用来存放push的东西，每次需要pop或者peek的时候，再将该栈的所有数据移到另外一个栈里。

class Queue {
public:
stack<int> Squeue1;
stack<int> Squeue2;
// Push element x to the back of queue.
void push(int x) {
Squeue1.push(x);
}

// Removes the element from in front of queue.
void pop(void) {

int q;
if(Squeue2.empty()){
while(!Squeue1.empty()){
q=Squeue1.top();
Squeue2.push(q);
Squeue1.pop();
}
}
Squeue2.pop();
}

// Get the front element.
int peek(void) {
int p,q;
if(Squeue2.empty()){
while(!Squeue1.empty()){
q=Squeue1.top();
Squeue2.push(q);
Squeue1.pop();
}
}
p=Squeue2.top();
return p;
}

// Return whether the queue is empty.
bool empty(void) {
if(Squeue1.empty()&&Squeue2.empty()) return true;
else return false;

}
};