public class Solution {
    private struct Solver {
        char[][] Board { get; init; }
        int Height { get => Board.Length; }
        int Width { get => Board[0].Length; }

        string Word { get; init; }

        public Solver(char[][] board, string word) {
            Board = board;
            Word = word;
        }

        private bool Has(int y, int x)
            => y >= 0 && y < Height && x >= 0 && x < Width;

        private bool DFS(int y, int x, int i) {
            if (i == Word.Length) {
                return true;
            }

            if (!Has(y, x) || Board[y][x] == '!' || Word[i] != Board[y][x]) {
                return false;
            }

            var tmp = Board[y][x];
            Board[y][x] = '!';

            foreach (int d in new int[] { 1, -1 }) {
                if (DFS(y + d, x, i + 1) || DFS(y, x + d, i + 1)) {
                    return true;
                }
            }

            Board[y][x] = tmp;
            return false;
        }

        public bool Solve() {
            for (int y = 0; y < Height; ++y) {
                for (int x = 0; x < Width; ++x) {
                    if (DFS(y, x, 0)) {
                        return true;
                    }
                }
            }

            return false;
        }
    }

    public bool Exist(char[][] board, string word) {
        return new Solver(board, word).Solve();
    }
}