pat甲级1107 并查集

并查集在findFather()函数中进行压缩路径，陷阱是这里只压缩该结点以上到根的路径，其以下的路径不压缩，这里不搞清楚会有三个测试点过不去

#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

int N;
vector<int> hobby[1001];
int father[1001];
int cluster[1001] = {};

int findFather(int a);
void unionElem(int a, int b);
bool cmp(int a, int b);

int main(){
    scanf("%d", &N);
    for(int i=1; i<=N; i++) father[i] = i; //并查集初始化
    for(int i=1; i<=N; i++){
        int ct, h;
        scanf("%d:", &ct);
        while(ct--){
            scanf("%d", &h);
            hobby[h].push_back(i);
        }
    }
    for(int i=1; i<=1000; i++){
        int n = hobby[i].size();
        for(int j=1; j<n; j++) unionElem(hobby[i][0], hobby[i][j]);
    }
    for(int i=1; i<=N; i++){
        cluster[findFather(i)]++; //必须用findFather(i)，不能用father[i]
    }
    sort(cluster, cluster+1001, cmp);
    int clu = 0;
    while(cluster[clu]>0) clu++;
    printf("%d\n", clu);
    for(int i=0; i<clu; i++){
        printf("%d", cluster[i]);
        if(i<clu-1) printf(" ");
    }

    return 0;
}

int findFather(int a){
    int x=a;
    while(father[a]!=a) a = father[a];
    while(father[x]!=x){
        //压缩该结点以上的路径
        int t=x;
        x = father[x];
        father[t] = a;
    }
    return a;
}

void unionElem(int a, int b){
    int fa = findFather(a);
    int fb = findFather(b);
    if(fa!=fb) father[fb] = fa;
    return;
}

bool cmp(int a, int b){
    return a>b;
}

来源：CSDN

作者：dantahejichi

链接：https://blog.csdn.net/sinat_37517996/article/details/104343458