class Solution {
public:
    int findCircleNum(vector<vector<int>>& M) {

        int n = (int)M.size();
        if(!n) return 0;

        int cnt_circle=0;

        vector<int>visit(n, 0);
        for(int i=0; i<n;i++)
        {
            if( !visit[i] )
            {
                dfs(i, visit, M);
                cnt_circle++;
            }
        }

        return cnt_circle;

    }

    void dfs(int node, vector<int>&visit, vector<vector<int>>&M)
    {
        visit[node] = 1;

        for( int i=0;i<(int)M[node].size();i++ )
        {
            if( !visit[i] && M[node][i] == 1)
            {
                dfs(i, visit, M);
            }
        }
    }
};