【leetcode】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.

 1 class MinStack {
 2 private:
 3     stack<int> stk;
 4     stack<int> minstack;
 5 public:
 6     void push(int x) {
 7         stk.push(x);
 8         if(minstack.empty())
 9         {
10             minstack.push(x);
11         }else
12         {
13             if(x<=minstack.top())
14                 minstack.push(x);
15         }
16     }
17
18     void pop() {
19         if(stk.top()==minstack.top())
20         {
21             stk.pop();
22             minstack.pop();
23         }else
24         {
25             stk.pop();
26         }
27     }
28
29     int top() {
30         return stk.top();
31     }
32
33     int getMin() {
34         return minstack.top();
35     }
36 };