Minesweeper LeetCode solution in Java

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class Solution {
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  public char[][] updateBoard(char[][] board, int[] click) {
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    int r = click[0];
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    int c = click[1];
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    if (board[r][c] == 'M') {
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      board[r][c] = 'X';
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      return board;
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    }
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    dfs(board, r, c);
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    return board;
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  }
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  private void dfs(char[][] board, int r, int c) {
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    if (r < 0
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        || r >= board.length
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        || c >= board[0].length
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        || c < 0
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        || board[r][c] == 'B') // Stop case
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    return;
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    int num = countMine(board, r, c); // count how many adjacent mines
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    if (num != 0) {
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      board[r][c] = (char) ('0' + num);
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      return;
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    } else {
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      board[r][c] = 'B';
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      dfs(board, r + 1, c); // recursively search all neighbors
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      dfs(board, r - 1, c);
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      dfs(board, r, c + 1);
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      dfs(board, r, c - 1);
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      dfs(board, r - 1, c - 1);
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      dfs(board, r + 1, c - 1);
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      dfs(board, r - 1, c + 1);
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      dfs(board, r + 1, c + 1);
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    }
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  }
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  private int countMine(char[][] board, int r, int c) {
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    int count = 0;
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    for (int i = r - 1; i <= r + 1; ++i) {
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      for (int j = c - 1; j <= c + 1; ++j) {
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        if (i >= 0 && i < board.length && j >= 0 && j < board[0].length) {
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          if (board[i][j] == 'M') count++;
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        }
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      }
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    }
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    return count;
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  }
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}