下一个更大元素（可循环）

 def nextGreaterElements(self, nums):
        """
        :type nums: List[int]
        :rtype: List[int]
        """
        # 做了两遍遍历，相当于循环
        dp = [-1] * len(nums)
        stack = []
        for i in range(len(nums)*2):
            while(len(stack) != 0 and nums[i%len(nums)] > nums[stack[-1]]):
                    dp[stack[-1]] = nums[i%len(nums)]
                    stack.pop()
            stack.append(i%len(nums))
        return dp

接雨水

每个柱子之间是没有空隙的

def trap(self, height):
        """
        :type height: List[int]
        :rtype: int
        """

        result=0

        stack=[0]
        
        for i in range(1,len(height)):
            if height[i] < height[stack[-1]]:
                stack.append(i)

            elif height[i] == height[stack[-1]]:
                stack.pop()
                stack.append(i)

            else:
                while len(stack) !=0 and height[i] > height[stack[-1]]:
                    cur_height=height[stack[-1]]
                    stack.pop()
                    if stack:
                        right_height=height[i]
                        left_height=height[stack[-1]]
                        h=min(left_height,right_height)-cur_height
                        w=i-stack[-1]-1
                        result += h*w
                
                stack.append(i)

        return result