leetcode155 Min Stack

思路：

最小值更新之前先把之前老的最小值存一份。

实现：

 1 class MinStack {
 2 public:
 3     /** initialize your data structure here. */
 4     int minn = INT_MAX;
 5     stack<int> s;
 6     MinStack() {
 7         
 8     }
 9     
10     void push(int x) {
11         if (x <= minn) {
12             s.push(minn);
13             minn = x;
14         }
15         s.push(x);
16     }
17     
18     void pop() {
19         if (s.top() == minn) { s.pop(); minn = s.top(); }
20         s.pop();
21     }
22     
23     int top() {
24         return s.top();
25     }
26     
27     int getMin() {
28         return minn;
29     }
30 };
31 
32 /**
33  * Your MinStack object will be instantiated and called as such:
34  * MinStack obj = new MinStack();
35  * obj.push(x);
36  * obj.pop();
37  * int param_3 = obj.top();
38  * int param_4 = obj.getMin();
39  */