1、前言

2、思路

3、代码

class MinStack {

    private Stack<Integer> stack1 = new Stack<Integer>();
    private Stack<Integer> stack2 = new Stack<Integer>();

    /** initialize your data structure here. */
    public MinStack() {

    }
    
    public void push(int x) {
        stack1.push(x);
        if(!stack2.isEmpty() && stack2.peek() < x){
            return;
        }
        stack2.push(x);
    }
    
    public void pop() {
        if(stack1.pop().equals(stack2.peek())){
            stack2.pop();
        }
    }
    
    public int top() {
        return stack1.peek();
    }
    
    public int min() {
        return stack2.peek();
    }
}