Never have I thought I will have to struggle with stacks. I have done things like: matching parens. I had done rain-water trapping before, but now it seems like an impossible feat.

The problem I am stuck at is the Next Greater Element:

Given distinct arrays nums1 (subset) and nums2.

- nums1=[4,1,2], nums2=[1,3,4,2] → [-1,3,-1]
- nums1=[2,4], nums2=[1,2,3,4] → [3,-1]

Its not the next greater value, but the immediate one
to the right

- nums1=[2,4], nums2=[1,2,4,3] → [4,-1]

The brute force can be like:

• Have a nums2_map with { num: index }
• for each num in nums1, find the value in the map
• and find the highest value within [index:n]

I don’t see much, here.