并查集  要判断这个图是连通的 就是只有一个父节点

#include 
    
     #include 
     
      #define maxn 100005int fa[maxn];bool ff[maxn];int findd( int x ){    return fa[x] == x ? x : fa[x] = findd(fa[x]);}void init(){    memset(ff, false, sizeof(ff));    for(int i = 1; i < maxn; i++)        fa[i] = i;}int main(){	//freopen("d://in.txt", "r", stdin);    int u,v,x,y,flag = 1;    init();    while(scanf("%d%d",&u,&v) == 2)    {        if(u == -1 && v == -1) break;        else if(u+v == 0)        {            int k = 0;            for(int i = 1; i < maxn; i++)            {                if(ff[i] && fa[i] == i)                    k++;            }            if(flag && k <= 1)                puts("Yes");            else                puts("No");            init();            flag = 1;        }        else        {            ff[u] = ff[v] = true;            x = findd(u), y = findd(v);            if(x != y)                fa[x] = y;            else                flag = 0;        }    }    return 0;}