题目：

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代码（首刷看解析）：

class Solution {
public:
    void dfs(vector<vector<int>>& isConnected,vector<int>& isVis,int i){
        int n = isConnected.size();
        for(int j=0;j<n;++j){
            if(isConnected[i][j]==1 && !isVis[j]){
                isVis[j]=1;
                dfs(isConnected,isVis,j);
            }
        }
    }
    int findCircleNum(vector<vector<int>>& isConnected) {
        int n = isConnected.size();
        vector<int> isVis(n);
        int provinces=0;
        for(int i=0;i<n;++i){
            if(!isVis[i]){
                dfs(isConnected,isVis,i);
                provinces++;
            }
        }
        return provinces;
    }
};