并查集

POJ 2524 Ubiquitous Religions

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
int n,m,maxnum;
int father[50005],num[50005];
void makeset(int n)//创建并查集
{
    for(int i=0;i<=n;i++){
        father[i]=i;//每个元素的father为自身
        num[i]=1;//每类均只有一个
    }
}
int findset(int x)
{
    if(father[x]!=x){
        father[x]=findset(father[x]);
    }
    return father[x];
}

void Union(int a,int b)
{
    int x=findset(a);
    int y=findset(b);
    if(x==y) return;
    if(num[x]<=num[y]){
        father[x]=y;
        num[y]+=num[x];
        maxnum--;
    }
    else{
        father[y]=x;
        num[x]+=num[y];
        maxnum--;
    }
}
int main()
{
    int Case=1;
    while(scanf("%d%d",&n,&m)!=EOF){
        if(n==0&&m==0) break;
        maxnum=n;
        makeset(n);
        int a,b;
        for(int i=0;i<m;i++){
            scanf("%d%d",&a,&b);
            Union(a,b);
        }
        printf("Case %d: %d\n",Case++,maxnum);
    }
    return 0;
}

HOJ 1225 - Supermarket

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
int h[10001];
struct product
{
    int p,d;
    bool operator < (const product &a){
       return a.p < p;
    }
}pd[10001];
inline int find(int x)
{//并查集查找 递归的路径压缩
    if (h[x]==x) return x;
    h[x]=find(h[x]);
    return h[x];
}
int main()
{
    int n;
    while(scanf("%d",&n)==1)
    {
        int ans=0;
        int md=0;//记录最大截止时间
        for (int i=1;i<=n;i++)
        {
            scanf("%d %d",&pd[i].p,&pd[i].d);
            if (md<pd[i].d) md=pd[i].d;
        }
        sort(pd+1,pd+n+1);//完全按价值从大到小排序,不考虑时间
        for (int i=0;i<=md;i++)
            h[i]=i;//初始化并查集，每个时间的最近空闲时间都是其本身
        //h[i]表示第i个单位时间内向前最近[保证尽量迟]是哪一个单位时间有空余
        for (int i=1;i<=n;i++){
            if (find(pd[i].d))
            {
                ans+=pd[i].p;
                h[h[pd[i].d]]=h[pd[i].d]-1;
                //将当前时间的最近空闲时间置为h[pd[i].d]-1
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}

HOJ 1564 - The Suspects

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
int h[30001];
int temp[30001];
int findset(int x)
{
    if(h[x]!=x){
        h[x]=findset(h[x]);
    }
    return h[x];
}
int main()
{
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF){
        if(n==0&&m==0) break;
        for(int i=0;i<n;i++){
           h[i]=i;
        }
        while(m--){
            int k;
            scanf("%d",&k);
            int mi=n;
            for(int i=0;i<k;i++){
                int x;
                scanf("%d",&x);
                temp[i]=findset(x);
                if(temp[i]<mi){
                    mi=temp[i];
                }
            }
            for(int i=0;i<k;i++){
                h[temp[i]]=mi;
            }
        }
        int num=0;
        for(int i=0;i<n;i++){
            if(findset(i)==0){
                num++;
            }
        }
        printf("%d\n",num);
    }
    return 0;
}

HOJ 1642 - Corporative Network

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
int father[20001],dis[20001];
inline int abs(int x){
    return x>0?x:-x;
}
int findset(int x)
{
    if(father[x]==x) return x;
    findset(father[x]);//更新沿途节点的距离值
    dis[x]+=dis[father[x]];
    father[x]=findset(father[x]);//路径上元素的父亲指针都指向根结点(路径压缩)
    return father[x];
}

void unionset(int x,int y){
    dis[x]=abs(x-y)%1000;
    father[x]=y;
}
int main() {
    int t;
    scanf("%d",&t);
    while(t--){
        int n;
        memset(dis, 0, sizeof(dis));
        scanf("%d",&n);
         for(int i=1;i<=n;i++){
            father[i]=i;
        }
        char op;
        while(scanf("%c",&op)&&op!='O'){
            if(op=='I'){
                int a,b;
                scanf("%d%d",&a,&b);
                unionset(a,b);
            }
            else if(op=='E'){
                int ans;
                scanf("%d",&ans);
                findset(ans);
                printf("%d\n",dis[ans]);
            }
        }
    }
    return 0;
}