Given an m x n 2D binary grid, grid which represents a map of '1's (land) and '0's (water), return the number of islands.

Autocomplete or suggestion or typeahead offers a number of possible values while typing. I am going to solve this problem using trie data structure and algorithm.

On a 2-dimensional grid, there are 4 types of squares. Return the number of 4-directional walks from the starting square to the ending square, that walk over every non-obstacle square exactly once.