力扣第200题 岛屿数量

力扣第200题 岛屿数量

 class Solution {
 public:
    int numIslands(vector<vector<char>>& grid)
    {
        int r[4]{0, 0, -1, 1};
        int l[4]{ -1, 1, 0, 0 };
        int res = 0;
        int len1 = grid.size();
        if (!len1)
            return res;
        int len2 = grid[0].size();
        queue<pair<int, int>> q;
        for (int i = 0; i < len1; i++)
        {
            for (int j = 0; j < len2; j++)
            {
                if (grid[i][j] == '1')
                {
                    q.push(pair<int, int>(i, j));
                    grid[i][j] = '0';
                    while (!q.empty())
                    {
                        pair<int, int> pr = q.front();
                        q.pop();
                        for (int k = 0; k < 4; k++)
                        {
                            int idx1 = pr.first + r[k];
                            int idx2 = pr.second + l[k];
                            if (idx1 >= 0 && idx1 < len1 && idx2 >= 0 && idx2 < len2 && grid[idx1][idx2] == '1')
                            {
                                q.push(pair<int, int>(idx1, idx2));
                                grid[idx1][idx2] = '0';
                            }
                        }
                    }
                    res++;
                }
            }
        }
        return res;
    }
};