void dfs(int u, vector<vector<int>> const& M, vector<bool>& visited) {

visited[u] = true;

for(int i = 0; i < (int)M[u].size(); i++) {

if(!M[u][i] or visited[i]) {

continue;

}

dfs(i, M, visited);

}

}

int findCircleNum(vector<vector<int>>& M) {

int n = (int)M.size();

vector<bool> visited(n, false);

int circle = 0;

for(int i = 0; i < n; i++) {

if(!visited[i]) {

circle++;

dfs(i, M, visited);

}

}

return circle;

}