MLE submissions:
https://leetcode.com/contest/leetcode-weekly-contest-56/submissions/detail/125773597/
https://leetcode.com/contest/leetcode-weekly-contest-56/submissions/detail/125774048/

AC submission:
https://leetcode.com/contest/leetcode-weekly-contest-56/submissions/detail/125774503/

I didn't expect we should to be so stringent on a solution with O(N^2) memory when N is a mere 1000. I suspect that LC judger somehow calculate the accumulated memory across multiple cases. I know if I use a global 2D array it will pass, and AFAIK the local STL vector style used to be passable.