【LeetCode】【HOT】155. 最小栈（辅助栈）

【LeetCode】【HOT】155. 最小栈

package hot;

import java.util.ArrayDeque;
import java.util.Deque;

public class Solution155 {
    public static void main(String[] args) {
        MinStack minStack = new MinStack();
        minStack.push(-2);
        minStack.push(0);
        minStack.push(-3);
        System.out.println(minStack.getMin());
        minStack.pop();
        System.out.println(minStack.top());
        System.out.println(minStack.getMin());
    }
}

class MinStack{
    Deque stack;
    Deque stack_min;

    public MinStack(){
        stack = new ArrayDeque<>();
        stack_min = new ArrayDeque<>();
    }

    public void push(int val){
        stack.push(val);
        if(stack_min.isEmpty() || val < stack_min.peek()){
            stack_min.push(val);
        }
    }

    public void pop(){
        if(stack.pop().equals(stack_min.peek())){
            stack_min.pop();
        }
    }

    public int top(){
        return stack.pop();
    }

    public int getMin(){
        return stack_min.pop();
    }
}

//时间复杂度为 O(1)
//空间复杂度为 O(n)