Q: 1 -> WORD SEARCH .

Code :

javaCopy codeclass Solution {
    public boolean exist(char[][] board, String word) {
        int row = board.length;
        int cols = board[0].length;
        for(int i = 0; i < row; i++){
            for(int j = 0; j < cols; j++){
                if(board[i][j] == word.charAt(0) && fn(board, word, i, j, 0, new boolean[row][cols])){
                    return true;
                }
            }
        }
        return false;
    }

    static boolean fn(char[][] grid, String word, int r, int c, int idx, boolean[][] visited) {
        // base case.
        if(idx == word.length()){
            return true;
        }
        if(r < 0 || r >= grid.length || c < 0 || c >= grid[0].length || word.charAt(idx) != grid[r][c] || visited[r][c]){
            return false;
        }
        // rec case.
        visited[r][c] = true;
        if(
            fn(grid, word, r + 1, c, idx + 1, visited) ||
            fn(grid, word, r - 1, c, idx + 1, visited) ||
            fn(grid, word, r, c + 1, idx + 1, visited) ||
            fn(grid, word, r, c - 1, idx + 1, visited)
        ){
            visited[r][c] = false;
            return true;
        }
        // back-track visited.
        visited[r][c] = false;
        return false;
    }
}