檢視題目

可以先求出矩陣的閉包，再判斷有幾個強連通圖 使用Floyd-Warshall演算法演算法求出閉包，一個強連通圖代表一個Circle

class Solution {
public:
    int findCircleNum(vector<vector<int>>& M) {
        int size = M.size();
        vector<vector<int> > M2(M);
        //求出閉包
        for (int k = 0; k < size; k ++) {
            for
 
 (int i = 0; i < size; i ++) {
                for (int j = 0; j < size; j ++) {
                    if (M2[i][k] && M2[k][j]) M2[i][j] = 1;
                }
            }
        }
        int cnt = 0;
        //判斷強連通圖的個數
        for (int i = 0; i < size; i ++) {
            if (M2[i][i]
 
 == 1) {
                cnt ++;
                M2[i][i] = 2;
                for (int j = i+1; j < size; j ++) {
                    if (M2[j][j] == 1 && M2[i][j] == 1) {
                        M2[j][j] = 2;
                    } 
                }
            }
            
        }
        return
 
 cnt;
    }
};