Word Search

DFS

public class Solution {
    public boolean exist(char[][] board, String word) {
        if(word == null || word.length() < 1)
            return false;
        HashSet<Integer> done = new HashSet<Integer>();
        
        for(int i = 0; i < board.length; i++)
            for(int j =0; j < board[0].length; j++){
                if(generate(board, i, j, 0, word, done))
                    return true;
            }
        
        return false;
    }
    
    private boolean generate(char[][] board, int row, int column, int depth, String word, HashSet<Integer> done){
        if(row < 0 || column < 0 || row >= board.length || column >= board[0].length)
            return false;
        int loc = row * board[0].length + column;
        if(done.contains(loc))
            return false;
        if(board[row][column] == word.charAt(depth)){
            if(depth == word.length()-1)
                return true;
            done.add(loc);
            if(generate(board, row+1, column, depth+1,word,done))
                return true;
            if(generate(board, row, column+1, depth+1,word,done))
                return true;
            if(generate(board, row-1, column, depth+1,word,done))
                return true;
            if(generate(board, row, column-1, depth+1,word,done))
                return true;
            done.remove(loc);
        }
        return false;
    }
}