[Leetcode] Word Search

Problem

Given a 2D board and a word, find if the word exists in the grid.

The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once.

For example,
Given board =

[
  ["ABCE"],
  ["SFCS"],
  ["ADEE"]
]

word = "ABCCED", -> returns true,
word = "SEE", -> returns true,
word = "ABCB", -> returns false.

Algorithm

A simple DFS algorithm works. Use a 2D visited array to record those visited letters. 

I misunderstood the question for a long time.
"adjacent" cells are those horizontally or vertically neighboring"
For a 3*3 array, element [0,0] is not a neighbor of element [0,2]. Why I made it so completed !

Code