深度优先搜索，遍历完一棵树之后，选择下一个没有mark的点继续搜索
class Solution {
public:
void countNum(vector<vector<int>>& M, int ith, bool marked[]) {
marked[ith] = true;
for(int i = 0; i < M.size(); i++) {
if(M[ith][i] == 1 && marked[i] == false) {
countNum(M, i, marked);
}
}
}
int findCircleNum(vector<vector<int>>& M) {
bool* markedNum = new bool[M.size()];
int circleNum = 0;
for(int i = 0; i < M.size(); i++)
markedNum[i] = false;
for(int i = 0; i < M.size(); i++) {
if(!markedNum[i]) {
countNum(M, i, markedNum);
circleNum++;
}
}
return circleNum;
}
};
