Given an m x n grid `board` of single-character strings and a string `word`, return true if `word` can be formed by a path of horizontally or vertically adjacent cells, where each cell is used at most once.
Figure
row · column
Examples
in: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABCCED"
out: true
path exists
Constraints
1 <= m, n <= 6 for tests
1 <= len(word) <= 15
board and word use uppercase letters
Hints
target: O(m*n*4^len(word)) time⌘↩ run · ⇧⌘↩ submit