剑指 Offer 30. 包含min函数的栈

思路

方法一：辅助栈 (单调栈)

 1 class MinStack {
 2 private:
 3     stack<int> A;
 4     stack<int> B;
 5 public:
 6     /** initialize your data structure here. */
 7     MinStack() {
 8         
 9     }
10     
11     void push(int x) {
12         A.push(x);
13         //这里不能写x < B.top()，否则下面这种输入过不了
14         /*
15             ["MinStack","push","push","push","getMin","pop","getMin"]
16             [[],[0],[1],[0],[],[],[]]
17         */
18         if(B.empty() || x <= B.top()) {
19             B.push(x);
20         }
21     }
22     
23     void pop() {
24         if(A.top() == B.top())
25             B.pop();
26         A.pop();
27     }
28     
29     int top() {
30         return A.top();
31     }
32     
33     int getMin() {
34         return B.top();
35     }
36 };
37 
38 /**
39  * Your MinStack object will be instantiated and called as such:
40  * MinStack* obj = new MinStack();
41  * obj->push(x);
42  * obj->pop();
43  * int param_3 = obj->top();
44  * int param_4 = obj->getMin();
45  */

方法二：一个栈同时保存当前值和栈内最小值

这里参考：一个栈同时保存当前值和栈内最小值

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