Battle over cities

图的遍历（DFS）
#include<cstdio>
#include<cstring>
#include<vector>
using namespace std;
const int N=1111;
vector<int>G[N];
bool vis[N];
int currentPoint;
void dfs(int v){
    if(v==currentPoint)return;
    vis[v]=true;
    for(int i=0;i<G[v].size();i++){
        if(vis[G[v][i]]==false){
            dfs(G[v][i]);
        }
    }
}
int n,m,k;
int main(){
    scanf("%d%d%d",&n,&m,&k);
    for(int i=0;i<m;i++){
        int a,b;
        scanf("%d%d",&a,&b);
        G[a].push_back(b);
        G[b].push_back(a);
    }
    for(int query=0;query<k;query++){
        scanf("%d",&currentPoint);
        memset(vis,false,sizeof(vis));
        int block=0;
        for(int i=1;i<=n;i++){
            if(i!=currentPoint&&vis[i]==false){
                dfs(i);
                block++;
            }
        }
        printf("%d\n",block-1);
    }
    return 0;
}
并查集
#include<cstdio>
#include<vector>
using namespace std;
const int N=1111;
vector<int>G[N];
int father[N];
bool vis[N];
int findFather(int x){
    int a=x;
    while(x!=father[x]){
        x=father[x];
    }
    while(a!=father[a]){
        int z=a;
        a=father[a];
        father[z]=x;
    }
    return x;
}
void Union(int a,int b){
    int faA=findFather(a);
    int faB=findFather(b);
    if(faA!=faB){
        father[faA]=faB;
    }
}
void init(){
    for(int i=1;i<N;i++){
        father[i]=i;
        vis[i]=false;
    }
}
int n,m,k;
int main(){
    scanf("%d%d%d",&n,&m,&k);
    for(int i=0;i<m;i++){
        int a,b;
        scanf("%d%d",&a,&b);
        G[a].push_back(b);
        G[b].push_back(a);
    }
    int currentPoint;
    for(int query=0;query<k;query++){
        scanf("%d",&currentPoint);
        init();
        for(int i=1;i<=n;i++){
            for(int j=0;j<G[i].size();j++){
                int u=i,v=G[i][j];
                if(u==currentPoint||v==currentPoint)continue;
                Union(u, v);
            }
        }
        int block=0;
        for(int i=1;i<=n;i++){
            if(i==currentPoint)continue;
            int fa_i=findFather(i);
            if(vis[fa_i]==false){
                block++;
                vis[fa_i]=true;
            }
        }
        printf("%d\n",block-1);
    }
    return 0;
}