leetcode/src/problems/LeetCode130.java at master · codinglin/leetcode · GitHub

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package problems;

import java.util.LinkedList;
import java.util.Queue;

/**
 * DFS
 */
public class LeetCode130 {
    int n, m;

    public void solve(char[][] board) {
        n = board.length;
        if (n == 0) {
            return;
        }
        m = board[0].length;
        for (int i = 0; i < n; i++) {
            dfs(board, i, 0);
            dfs(board, i, m - 1);
        }
        for (int i = 1; i < m - 1; i++) {
            dfs(board, 0, i);
            dfs(board, n - 1, i);
        }
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (board[i][j] == 'A') {
                    board[i][j] = 'O';
                } else if (board[i][j] == 'O') {
                    board[i][j] = 'X';
                }
            }
        }
    }

    public void dfs(char[][] board, int x, int y) {
        if (x < 0 || x >= n || y < 0 || y >= m || board[x][y] != 'O') {
            return;
        }
        board[x][y] = 'A';
        dfs(board, x + 1, y);
        dfs(board, x - 1, y);
        dfs(board, x, y + 1);
        dfs(board, x, y - 1);
    }
}

/**
 * BFS
 */
class LeetCode130_1 {
    int[] dx = {1, -1, 0, 0};
    int[] dy = {0, 0, 1, -1};

    public void solve(char[][] board) {
        int n = board.length;
        if(n == 0) {
            return;
        }
        int m = board[0].length;
        Queue<int[]> queue = new LinkedList<int[]>();
        for (int i = 0; i < n; i++) {
            if (board[i][0] == 'O') {
                queue.offer(new int[]{i, 0});
                board[i][0] = 'A';
            }
            if (board[i][m - 1] == 'O') {
                queue.offer(new int[]{i, m - 1});
                board[i][m - 1] = 'A';
            }
        }
        for (int i = 1; i < m - 1; i++) {
            if (board[0][i] == 'O') {
                queue.offer(new int[]{0, i});
                board[0][i] = 'A';
            }
            if (board[n - 1][i] == 'O') {
                queue.offer(new int[]{n - 1, i});
                board[n - 1][i] = 'A';
            }
        }
        while (!queue.isEmpty()) {
            int[] cell = queue.poll();
            int x = cell[0], y = cell[1];
            for (int i = 0; i < 4; i++) {
                int mx = x + dx[i], my = y + dy[i];
                if (mx < 0 || my < 0 || mx >= n || my >= m || board[mx][my] != 'O') {
                    continue;
                }
                queue.offer(new int[]{mx, my});
                board[mx][my] = 'A';
            }
        }
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (board[i][j] == 'A') {
                    board[i][j] = 'O';
                } else if (board[i][j] == 'O') {
                    board[i][j] = 'X';
                }
            }
        }
    }
}