unreasonably effective

class Solution:
    def nextGreaterElement(self, nums1: List[int], nums2: List[int]) -> List[int]:
        next_greater = {}
        stack = []
        for x in nums2:
            while stack and x > (top := stack[-1]):
                next_greater[top] = x
                stack.pop()
            stack.append(x)
        # Throw away numbers without a next greater element
        stack = None

        ans = []
        for x in nums1:
            ans.append( next_greater.get(x, -1) )
        return ans