Lintcode: Implement Queue by Two Stacks

As the title described, you should only use two stacks to implement a queue's actions.

The queue should support push(element), pop() and top() where pop is pop the first(a.k.a front) element in the queue.

Both pop and top methods should return the value of first element.

Have you met this question in a real interview? 

Yes

Example

For push(1), pop(), push(2), push(3), top(), pop(), you should return 1, 2 and 2

Challenge

implement it by two stacks, do not use any other data structure and push, pop and top should be O(1) by AVERAGE.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

class Queue { public: stack<int> stack1; stack<int> stack2; Queue() { // do intialization if necessary } void push(int element) { // write your code here stack1.push(element); } int pop() { // write your code here move(); int res; res = stack2.top(); stack2.pop(); return res; } int top() { // write your code here int res; move(); res = stack2.top(); return res; } private: void move(){ if(!stack2.empty()) return; while(!stack1.empty()){ int temp; temp = stack1.top(); stack1.pop(); stack2.push(temp); } } };