POJ2912-并查集

这题是POJ1182食物链的升级版，先做那题，这题应该也没问题了。

#include <cstdio>
#include <cstring>
#include <iostream>
using namespace std;

const int NN=550;
const int MM=2100;

int n,m;
struct Rec{
    int a,b,c;
    Rec() {}
    Rec(int _a,int _b,int _c): a(_a),b(_b),c(_c) {}
}e[MM];

int p[NN],r[NN];
int find(int x)
{
    if (p[x]!=x)
    {
        int t=p[x];
        p[x]=find(p[x]);
        r[x]=(r[x]+r[t])%3;
    }
    return p[x];
}

inline void Union(int c,int a,int b)
{
    int x=find(a);
    int y=find(b);
    p[x]=y;
    r[x]=(r[b]-r[a]+c+3)%3;
}

int err[NN];
void solve()
{
    int a,b,c,J,cnt=0,last=0;
    memset(err,0,sizeof(err));
    for (int k=1; k<=n; k++)
    {
        for (int i=1; i<=n; i++)
        {
            p[i]=i;
            r[i]=0; //0: the same  1: eat  2: be eated
        }
        for (int t=1; t<=m && !err[k]; t++)
        {
            a=e[t].a; b=e[t].b; c=e[t].c;
            if (a==k || b==k) continue;

            if (find(a)!=find(b)) Union(c,a,b);
            else if ((r[b]+c)%3!=r[a]) err[k]=t;
        }
        if (err[k])
        {
            cnt++;
            last=max(last,err[k]);
        }
        else J=k;
    }

    if (cnt<n-1)
        printf("Can not determine\n");
    else if (cnt==n)
        printf("Impossible\n");
    else
        printf("Player %d can be determined to be the judge after %d lines\n",J-1,last);
}

int main()
{
    int a,b;
    char ope;
    while (~scanf("%d%d",&n,&m))
    {
        for (int i=1; i<=m; i++)
        {
            scanf("%d%c%d",&a,&ope,&b);
            a++,b++;
            if (ope=='=')      e[i]=Rec(a,b,0);
            else if (ope=='>') e[i]=Rec(a,b,1);
            else               e[i]=Rec(b,a,1);
        }
        solve();
    }
    return 0;
}