155. 最小栈

 1 package basic.queue_stack;
 2 
 3 import java.util.Stack;
 4 
 5 public class MinStack {
 6     private Stack<Integer> dataStack;
 7     private Stack<Integer> minStack;
 8     private int min;
 9     
10     public MinStack() {
11         dataStack = new Stack<>();
12         minStack = new Stack<>();
13         min = Integer.MAX_VALUE;
14     }
15     
16     public void push(int item) {
17         dataStack.push(item);
18         min = Math.min(min, item);  //两个栈中的数据总数始终相等，弹栈时无需比较，minStack可以直接弹栈
19         minStack.push(min);
20     }
21     
22     public void pop() {
23         dataStack.pop();
24         minStack.pop();
25         min = minStack.isEmpty() ? Integer.MAX_VALUE : minStack.peek();
26     }
27     
28     public int top() {
29         return dataStack.peek();
30     }
31     
32     public int getMin() {
33         return minStack.peek();
34     }
35 }