Implement `editDistance(a, b)` returning the minimum number of single-character insertions, deletions, or substitutions needed to turn string `a` into string `b` (the Levenshtein distance).
+ 2 hidden tests run on Submit.
Classic two-dimensional DP. The base row/column encode turning a prefix into the empty string. Each cell either inherits the diagonal on a match or adds one operation to the cheapest neighbour. O(m × n) time and space.
Run your code to see results.