Min Stack

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• getMin() -- Retrieve the minimum element in the stack.

利用栈来存储最小值

1. class MinStack {
2. public:
3. void push(int x) {
4. data.push(x);
5. if(min.empty()) min.push(x);
6. else if(x<=min.top()) {
7. min.push(x);
8. }
9. }
10. void pop() {
11. if(data.empty()) {
12. return;
13. }
14. int top = data.top();
15. if(top == min.top()) {
16. min.pop();
17. }
18. data.pop();
19. }
20. int top() {
21. if(!data.empty())
22. return data.top();
23. return -1;
24. }
25. int getMin() {
26. if(min.empty()) {
27. return -1;
28. }
29. return min.top();
30. }
31. private:
32. stack<int> data;
33. stack<int> min;
34. };