题解 | #单调栈#

只需一次遍历：

class Solution:
    def foundMonotoneStack(self , nums: List[int]) -> List[List[int]]:
        stack = []
        ans = [[-1, -1] for _ in range(len(nums))]

        for i in range(len(nums)):
            while stack and nums[stack[-1]] > nums[i]:
                ans[stack[-1]][1] = i
                stack.pop()
            if stack:
                if nums[stack[-1]] < nums[i]:
                    ans[i][0] = stack[-1]
                elif nums[stack[-1]] == nums[i]:
                    ans[i][0] = ans[stack[-1]][0]
            stack.append(i)
        return ans