1080. Map Coloring

http://acm.timus.ru/problem.aspx?space=1&num=1080

dfs 水题不解释

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

#define LL long long

using namespace std;

const int N=103;
int head[N];
struct node
{
    int j,next;
}side[N*N];
int I;
int ans;
int color[N];
void build(int i,int j)
{
    side[I].j=j;
    side[I].next=head[i];
    head[i]=I++;
}

void dfs(int x,int k)
{
    if(color[x]!=-1)
    {
        if(color[x]!=k)
        ans=-1;
        return ;
    }
    color[x]=k;
    for(int t=head[x];t!=-1;t=side[t].next)
    {
        int l=side[t].j;
        dfs(l,(k?0:1));
        if(ans==-1)
        return ;
    }
}
int main()
{
    //freopen("data.txt","r",stdin);
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        memset(head,-1,sizeof(head));
        I=0;
        for(int i=1;i<=n;++i)
        {
            int j;
            while(scanf("%d",&j),j)
            {
                build(i,j);
                build(j,i);
            }
        }
        ans=0;
        memset(color,-1,sizeof(color));
        dfs(1,0);
        if(ans==-1)
        {printf("-1\n");continue;}
        for(int i=1;i<=n;++i)
        printf("%d",color[i]);
        printf("\n");
    }
    return 0;
}