题目：https://pintia.cn/problem-sets/994805342720868352/problems/994805500414115840
标准图的DFS写法，最好看一下，难度不是很大

代码

  1. #include<vector>
  2. #include<algorithm>
  3. #include<iostream>
  4. #include<cstring>
  5. #include<cstdio>
  6. using namespace std;
  7. const int N = 1111;
  8. vector<int> G[N];//邻接表
  9. bool vis[N];
  10. int current_point;
  12. void dfs(int v){
  13.     if(v == current_point) return;
  14.     vis[v] = true;
  15.     for(int i = 0; i < G[v].size(); i++){
  16.         if(vis[G[v][i]] == false) dfs(G[v][i]);
  17.     }
  18. }
  20. int main(){
  21.     int n, m, k;
  22.     scanf("%d %d %d", &n, &m, &k);
  23.     for(int i = 0; i < m; i++){
  24.         int a,b;
  25.         scanf("%d%d", &a, &b);
  26.         G[a].push_back(b);//a的边里面有b
  27.         G[b].push_back(a);
  28.     }
  30.     for(int i = 0; i < k; i++){
  31.         scanf("%d", &current_point);
  32.         memset(vis, false, sizeof(vis));
  33.         int block = 0;//连通块个数
  34.         for(int i = 1; i <= n; i++){
  35.             if(i != current_point && vis[i] == false){
  36.                 dfs(i);
  37.                 block++;
  38.             }
  39.         }
  40.         printf("%d\n", block - 1);
  41.     }
  42. }