推荐这个视频动画详解,看后就明白了:https://www.bilibili.com/video/av498397425/
  
class Solution:
    def temperatures(self,tem_arr):
        tem_arr_len = len(tem_arr)
        res = [0]*tem_arr_len
        stack = []
        for i in range(tem_arr_len):
            temp = tem_arr[i]
            while stack and temp > tem_arr[stack[-1]]:
                top_index = stack.pop()
                res[top_index] = i - top_index
            stack.append(i)
        return res