Zju1015 Fishing Net

　　弦图判定

　　代码

 1 #include<cstdio>
 2 #include<queue>
 3 #define mp make_pair
 4 #define fi first
 5 #define sc second
 6 using namespace std;
 7 const int N = 2001010;
 8 int n,m,a,b,i,j;
 9 int dp,p[N],pre[N],tt[N],o,vis[N],sum[N],id[N],ID[N];
10 priority_queue<pair<int,int> > Q;
11 void link(int x,int y)
12 {
13     dp++;pre[dp]=p[x];p[x]=dp;tt[dp]=y;
14 }
15 int main()
16 {
17     scanf("%d%d",&n,&m);
18     for (i=1;i<=m;i++)
19     {
20         scanf("%d%d",&a,&b);
21         link(a,b);
22         link(b,a);
23     }
24     for (i=1;i<=n;i++)
25     Q.push(mp(0,i));
26     o=n;
27     while (!Q.empty())
28     {
29         int x=Q.top().fi;
30         int y=Q.top().sc;
31         Q.pop();
32         if (vis[y]) continue;
33         if (x<sum[y]) continue;
34         ID[y]=o;
35         id[o--]=y;
36         vis[y]=1;
37         i=p[y];
38         while (i)
39         {
40             if (!vis[tt[i]])
41             {
42                 sum[tt[i]]++;
43                 Q.push(mp(sum[tt[i]],tt[i]));
44             }
45             i=pre[i];
46         }
47     }
48     for (i=1;i<=n;i++) vis[i]=0;
49
50     for (j=1;j<=n;j++)
51     {
52         int x=id[j],cnt1=0,cnt2=0,mi=0x37373737,y=0;
53         i=p[x];
54         while (i)
55         {
56             if (ID[tt[i]]>j)
57             {
58                 if (ID[tt[i]]<mi) mi=ID[tt[i]],y=tt[i];
59                 vis[tt[i]]=1;cnt1++;
60             }
61             i=pre[i];
62         }
63
64         if (y)
65         {
66             i=p[y];
67             while (i)
68             {
69                 if (vis[tt[i]]) cnt2++;
70                 i=pre[i];
71             }
72         }
73         if ((cnt1!=cnt2+1)&&(y))
74         {
75             printf("Imperfect");
76             return 0;
77         }
78         i=p[x];
79         while (i)
80         {
81             vis[tt[i]]=0;
82             i=pre[i];
83         }
84     }
85     printf("Perfect");
86 }