Jan 21 - Word Search; BackTracking; Array; DFS;

Use DFS to find the possible path that match the string;

Code:

public class Solution {
    public boolean exist(char[][] board, String word) {
        if(word == null) return false;
        int row = board.length;
        int col = board[0].length;
        int count = word.length();
        boolean flag = false;
        for(int i = 0; i < row; i++){
            for(int j = 0; j < col; j++){
                if(board[i][j] == word.charAt(0)){
                    boolean[][] mark = new boolean[row][col];
                    if(checkLetter(count-1, word, 0, board, i, j, row, col, mark)) return true;
                }
            }
        }
        return false;
    }
    
    public boolean checkLetter(int n, String s, int i, char[][] board, int x, int y, int row, int col, boolean[][] isMarked){
        char letter = s.charAt(i);
        char c = board[x][y];
        boolean flag = false;
        if(letter != c) return false;
        else{
            isMarked[x][y] = true;
            if(i == n) return true;
            if((x+1) < row && !isMarked[x+1][y]) {
                if(checkLetter(n, s, i+1, board, x+1, y, row, col, isMarked)) return true; 
            }
            if((x-1) >= 0 && !isMarked[x-1][y]) {
                if(checkLetter(n, s, i+1, board, x-1, y, row, col, isMarked)) return true; 
            }
            if((y+1) < col && !isMarked[x][y+1]) {
                if(checkLetter(n, s, i+1, board, x, y+1, row, col, isMarked)) return true; 
            }
            if((y-1) >= 0 && !isMarked[x][y-1]) {
                if(checkLetter(n, s, i+1, board, x, y-1, row, col, isMarked)) return true; 
            }
            isMarked[x][y] = false;
            return false;
        }
    }
}