Minesweeper.java

// https://leetcode.com/problems/minesweeper/
// #dfs #bfs
class Solution {

  public char[][] updateBoard(char[][] board, int[] click) {

    Node root = new Node(click[0], click[1]);
    Deque<Node> queue = new LinkedList<>();
    queue.addLast(root);

    // corner case
    if (board[root.x][root.y] == 'M') {
      board[root.x][root.y] = 'X';
      return board;
    }

    // normal case
    while (!queue.isEmpty()) {
      Node node = queue.pollLast();

      // update value at node
      int mineCount = 0;
      for (int i = 0; i < 8; i++) {
        int x = dx[i] + node.x;
        int y = dy[i] + node.y;
        if (isValidSquare(board, x, y) && board[x][y] == 'M') {
          mineCount++;
        }
      }
      if (mineCount == 0) {
        board[node.x][node.y] = 'B';
      } else {
        board[node.x][node.y] = (char) (mineCount + '0');
        continue;
      }

      // add neighbour to the queue
      for (int i = 0; i < 8; i++) {
        int x = dx[i] + node.x;
        int y = dy[i] + node.y;
        if (isValidSquare(board, x, y) && board[x][y] == 'E') {
          queue.addLast(new Node(x, y));
        }
      }
    }
    return board;
  }

  private static boolean isValidSquare(char[][] board, int x, int y) {
    if (x < 0 || x >= board.length) {
      return false;
    }
    if (y < 0 || y >= board[0].length) {
      return false;
    }
    return true;
  }

  private static int[] dx = {-1, 0, 1, -1, 1, -1, 0, 1};
  private static int[] dy = {-1, -1, -1, 0, 0, 1, 1, 1};

  private static class Node {
    int x;
    int y;

    Node(int x, int y) {
      this.x = x;
      this.y = y;
    }
  }
  ;
}