Graph — Path With Minimum Effort

solve(heights) — you start at the top-left cell of a grid and want to reach the
bottom-right cell, moving up, down, left or right. The effort of a path is the
largest absolute height difference between two consecutive cells on it. Return the
minimum effort over all paths.

This is Dijkstra with a twist: the "distance" of a path is the maximum edge on
it instead of the sum, and it still works because extending a path can never lower
it. A MinHeap ordered by item[0] is provided for JavaScript and TypeScript;
Python has heapq.

Examples

solve([[1,2,2],[3,8,2],[5,3,5]])                                   → 2
solve([[1,2,3],[3,8,4],[5,3,5]])                                   → 1
solve([[1,2,1,1,1],[1,2,1,2,1],[1,2,1,2,1],[1,2,1,2,1],[1,1,1,2,1]]) → 0
solve([[1]])                                                       → 0