79-Word-Search.java

//This is a typical backtracking problem similar to Number of Islands.
//In number of Isalnds, we sinked the islands. Here, we will do the same by adding changing the value of the char.
//I added 100 because it will exceed the ascii limit for characters and will change it to some ascii value which is not an alphabet.

class Solution {

    public boolean exist(char[][] board, String word) {
        int m = board.length;
        int n = board[0].length;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (check(board, word, i, j, m, n, 0)) {
                    return true;
                }
            }
        }
        return false;
    }

    public boolean check(
        char[][] board,
        String word,
        int i,
        int j,
        int m,
        int n,
        int cur
    ) {
        if (cur >= word.length()) return true;
        if (
            i < 0 ||
            j < 0 ||
            i >= m ||
            j >= n ||
            board[i][j] != word.charAt(cur)
        ) return false;
        boolean exist = false;
        if (board[i][j] == word.charAt(cur)) {
            board[i][j] += 100;
            exist =
                check(board, word, i + 1, j, m, n, cur + 1) ||
                check(board, word, i, j + 1, m, n, cur + 1) ||
                check(board, word, i - 1, j, m, n, cur + 1) ||
                check(board, word, i, j - 1, m, n, cur + 1);
            board[i][j] -= 100;
        }
        return exist;
    }
}