Leetcode 155. 最小栈

class MinStack {
    //用一个辅助栈存储对应栈元素为栈顶时的最小值
    //当原栈插入一个元素时，辅助栈插入此值与当前辅助栈栈顶的值（即插入前的最小值）的较小值
    Stack sta1;
    Stack sta2;
    public MinStack() {
        sta1 = new Stack();
        sta2 = new Stack();
        sta2.push(Integer.MAX_VALUE);
    }
    
    public void push(int val) {
        sta1.push(val);
        sta2.push(Math.min(val, sta2.peek()));
    }
    
    public void pop() {
        sta1.pop();
        sta2.pop();
    }
    
    public int top() {
        return sta1.peek();
    }
    
    public int getMin() {
        return sta2.peek();
    }
}
 
/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack obj = new MinStack();
 * obj.push(val);
 * obj.pop();
 * int param_3 = obj.top();
 * int param_4 = obj.getMin();
 */