50 DSA-Questions: #14 Word Search

#14. Word Search

Given an m x n grid of characters board and a string word, return true if the word exists in the grid. The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once.

class Solution {
    public boolean exist(char[][] board, String word) {
        for (int i=0; i<board.length; i++) {
            for (int j=0; j<board[0].length; j++) {
                boolean found = searchWordDFS(board, i, j, 0, word, "#");
                if (found) {
                    return true;
                }
            }
        }
        return false;
    }
    private boolean isCellFit(char[][] board, int i, int j, int wordPos, String word, String visited) {
        if (i < 0 || i >= board.length || j < 0 || j >= board[0].length || wordPos >= word.length()) {
            return false; // out of grid
        }
        int index = i * board[0].length + j;
        if (visited.contains("#" + index + "#")) {
            return false; // already been there
        }
        
        return board[i][j] == word.charAt(wordPos);
    }
    private boolean searchWordDFS(char[][] board, int i, int j, int wordPos, String word, String visited) {
        // Este important de tinut visited ca String si nu ca List/alt obiect pentru a fi pasat prin valoare, 
        // nu prin referinta, astfel incat, la intoarcerea fara succes din recursivitate indecsii din matrice
        // vizitati sa fie abandonati
        if (isCellFit(board, i, j, wordPos, word, visited)) {
            visited += (i * board[0].length + j) + "#";
            if (wordPos == word.length() - 1) {
                return true;
            }
            
            boolean found = searchWordDFS(board, i, j + 1, wordPos + 1, word, visited); // right
            if (!found) {
                found = searchWordDFS(board, i, j - 1, wordPos + 1, word, visited); // left
            }
            if (!found) { 
                found = searchWordDFS(board, i + 1, j, wordPos + 1, word, visited); // down
            }
            if (!found) {
                found = searchWordDFS(board, i - 1, j, wordPos + 1, word, visited); // up
            }
            return found;
        }
        return false;
    }
}