# 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.

## Example

Given board =

[
"ABCE",
"SFCS",
]
• word = "ABCCED", -> returns true,
• word = "SEE", -> returns true,
• word = "ABCB", -> returns false.

## Code - Java

public class Solution {
/**
* @param board: A list of lists of character
* @param word:  A string
* @return: A boolean
*/
public boolean exist(char[][] board, String word) {
// write your code here
if (board.length == 0 || board[0].length == 0) return false;
int lenX = board.length;
int lenY = board[0].length;

boolean[][] visited = new boolean[lenX][lenY];

for (int i = 0; i < lenX; i++) {
for (int j = 0; j < lenY; j++) {
if (search(board, visited, word.toCharArray(), 0, i, j)) {
return true;
}
}
}
return false;
}

private boolean search(char[][] board, boolean[][] visited, char[] word, int wordIndex, int x, int y) {
if (visited[x][y] == true) {
return false;
}

if (board[x][y] != word[wordIndex]) {
return false;
}
if (wordIndex == word.length - 1) {
return true;
}
visited[x][y] = true;
if (x > 0 && search(board, visited, word, wordIndex + 1, x - 1, y)) {
return true;
}

if (x < board.length - 1 && search(board, visited, word, wordIndex + 1, x + 1, y)) {
return true;
}

if (y > 0 && search(board, visited, word, wordIndex + 1, x, y - 1)) {
return true;
}

if (y < board[0].length - 1 && search(board, visited, word, wordIndex + 1, x, y + 1)) {
return true;
}
visited[x][y] = false;
return false;
}
}