1013 Battle Over Cities (25 分)（并查集，图）（******）

//图的遍历
#include <cstdio>
#include <queue>
#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;
const int maxv = 2011,inf = 1<<30;
//int G[maxv][maxv] = {0};
vector<int>G[maxv];
int n,m,k;
bool vis[maxv] = {false};

int current;

void Dfs(int v)
{
    if(v==current) return;
    vis[v] = true;
    for(int i = 0;i<G[v].size();i++)
    {
        if(vis[G[v][i]] == false)
            Dfs(G[v][i]);
    }
}

void dfsTra(int& ans)
{
    for(int i = 1;i<=n;i++)
    {
        if(vis[i] == false && i!=current)
        {
            Dfs(i);
            ans++;
        }
    }
}



int main()
{
    scanf("%d%d%d",&n,&m,&k);
    for(int i = 1;i<=m;i++)
    {
        int id1,id2;
        scanf("%d%d",&id1,&id2);
        G[id1].push_back(id2);
        G[id2].push_back(id1);
    }


    for(int i = 1;i<=k;i++)
    {
        scanf("%d",&current);
        int ans = 0;
//        fill(vis,vis+maxv,0);
        memset(vis,false,sizeof(vis));
        dfsTra(ans);
        printf("%d\n",ans-1);
    }



    return 0;
}

并查集
#include <cstdio>
#include <queue>
#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;
const int maxv = 2011,inf = 1<<30;
int father[maxv];
vector<int>G[maxv];
int n,m,k;
bool vis[maxv] = {false};

int current;

void init()
{
    for(int i = 1;i<=n;i++)
    {
        father[i] = i;
        vis[i] = false;
    }
}

int findFather(int x)
{
    int a = x;
    while(father[x] != x)
        x = father[x];
    while(father[a] != a)
    {
        int z = a;
        father[a] = x;
        a = father[z];
    }
    return x;
}

void unit(int a,int b)
{
    int faA = findFather(a);
    int faB = findFather(b);
    if(faA != faB)
        father[faA] = faB;
}

int main()
{
    freopen("1.txt","r",stdin);
    scanf("%d%d%d",&n,&m,&k);
    for(int i = 1;i<=m;i++)
    {
        int id1,id2;
        scanf("%d%d",&id1,&id2);
        G[id1].push_back(id2);
        G[id2].push_back(id1);
    }


    for(int i = 1;i<=k;i++)
    {
        scanf("%d",&current);
        init();//?
        for(int j = 1;j<=n;j++)
        {
            for(int z = 0;z<G[j].size();z++)
            {
                int u = j,v=G[j][z];
                if(u == current || v== current) continue;//?
                unit(u,v);
            }
        }
            int ans = 0;
            for(int z = 1;z<=n;z++)
            {
                if(z==current) continue;//?
                if(vis[findFather(z)]==false)
                {
                    vis[findFather(z)] = true;
                    ans++;
                }
            }
            printf("%d\n",ans-1);

    }



    return 0;
}