695.岛屿的最大面积 (Medium)*

class Solution {
    int dfs(vector<vector<int>>& grid, int i, int j) {
        if(i < 0 || j < 0 || i >= grid.size() || j >= grid[0].size() || grid[i][j] != 1) {
            return 0;
        }
        grid[i][j] = 2;
        return dfs(grid, i + 1, j) + dfs(grid, i - 1, j) +
            dfs(grid, i, j + 1) + dfs(grid, i, j - 1) + 1;
    }
public:
    int maxAreaOfIsland(vector<vector<int>>& grid) {
        int res = 0;
        for(int i = 0; i < grid.size(); i++) {
            for(int j = 0; j < grid[0].size(); j++) {
                if(grid[i][j] == 1) {
                    int cur = dfs(grid, i, j);
                    if(cur > res) {
                        res = cur;
                    }
                }
            }
        }
        return res;
    }
};

class Solution {
    int bfs(vector<vector<int>>& grid, int i, int j, int rows, int cols) {
        // 二维转一维
        queue<int> q;
        q.push(i * cols + j);
        int cnt = 0;
        while(!q.empty()) {
            int cur = q.front();
            q.pop();
            int row = cur / cols;
            int col = cur % cols;
            if(grid[row][col] == 2) {
                continue;
            }
            // 判断 当前为 1 才加 1
            cnt++;
            grid[row][col] = 2;
            if(row != rows - 1 && grid[row + 1][col] == 1) {
                q.push((row + 1) * cols + col);
            }
            if(row != 0 && grid[row - 1][col] == 1) {
                q.push((row - 1) * cols + col);
            }
            if(col != cols - 1 && grid[row][col + 1] == 1) {
                q.push(row * cols + col + 1);
            }
            if(col != 0 && grid[row][col - 1] == 1) {
                q.push(row * cols + col - 1);
            }
        }
        return cnt;
    }
public:
    int maxAreaOfIsland(vector<vector<int>>& grid) {
        int rows = grid.size();
        int cols = grid[0].size();
        int res = 0;
        for(int i = 0; i < rows; i++) {
            for(int j = 0; j < cols; j++) {
                if(grid[i][j] == 1) {
                    int cur = bfs(grid, i, j, rows, cols);
                    if(cur > res) {
                        res = cur;
                    }
                }
            }
        }
        return res;
    }
};