洛谷.1333.瑞瑞的木棍(欧拉路径 Hash)

#include <cstdio>
#include <cstring>
const int N=2e6+5,M=5e5+5,mod=2e6;
const int seed[5]={31,37,131,41};

int dgr[N],fa[M];
char s[15];
namespace Hash
{
    int cnt,val[N],pos[N];
    int Get_Hash(char *s)
    {
        int x=0,l=strlen(s);
        for(int i=0; i<l; ++i) x=(x+s[i]*seed[i%4])%mod;
        return x;
    }
    int Insert(char *s)
    {
        int p=Get_Hash(s);
        while(val[p]&&val[p]!=p){
            ++p;
            if(p>=mod) p-=mod;
        }
        if(val[p]) return pos[p];
        val[p]=p;
        return pos[p]=++cnt;
    }
}
int Find(int x){
    return x==fa[x]?x:fa[x]=Find(fa[x]);
}

int main()
{
    int p1,p2,r1,r2,t=0;
    for(int i=1; i<M; ++i) fa[i]=i;
    while(~scanf("%s",s))
    {
        p1=Hash::Insert(s);
        scanf("%s",s);
        p2=Hash::Insert(s);
        ++dgr[p1], ++dgr[p2];
        r1=Find(p1), r2=Find(p2);
        if(r1!=r2) ++t,fa[r1]=r2;
    }
    if(t<Hash::cnt-1) {printf("Impossible"); return 0;}
    int tot=Hash::cnt; t=0;
    for(int i=1; i<=tot; ++i)
        if(dgr[i]&1) ++t;
    printf(t>2?"Impossible":"Possible");

    return 0;
}