ZOJ2587 Unique Attack（判定最小割唯一性）

  1 #include<cstdio>
  2 #include<cstring>
  3 #include<queue>
  4 #include<algorithm>
  5 using namespace std;
  6 #define INF (1<<30)
  7 #define MAXN 888 
  8 #define MAXM 40000 
  9 
 10 struct Edge{
 11     int v,cap,flow,next;
 12 }edge[MAXM];
 13 int vs,vt,NE,NV;
 14 int head[MAXN];
 15 
 16 void addEdge(int u,int v,int cap){
 17     edge[NE].v=v; edge[NE].cap=cap; edge[NE].flow=0;
 18     edge[NE].next=head[u]; head[u]=NE++;
 19     edge[NE].v=u; edge[NE].cap=0; edge[NE].flow=0;
 20     edge[NE].next=head[v]; head[v]=NE++;
 21 }
 22 
 23 int level[MAXN];
 24 int gap[MAXN];
 25 void bfs(){
 26     memset(level,-1,sizeof(level));
 27     memset(gap,0,sizeof(gap));
 28     level[vt]=0;
 29     gap[level[vt]]++;
 30     queue<int> que;
 31     que.push(vt);
 32     while(!que.empty()){
 33         int u=que.front(); que.pop();
 34         for(int i=head[u]; i!=-1; i=edge[i].next){
 35             int v=edge[i].v;
 36             if(level[v]!=-1) continue;
 37             level[v]=level[u]+1;
 38             gap[level[v]]++;
 39             que.push(v);
 40         }
 41     }
 42 }
 43 
 44 int pre[MAXN];
 45 int cur[MAXN];
 46 int ISAP(){
 47     bfs();
 48     memset(pre,-1,sizeof(pre));
 49     memcpy(cur,head,sizeof(head));
 50     int u=pre[vs]=vs,flow=0,aug=INF;
 51     gap[0]=NV;
 52     while(level[vs]<NV){
 53         bool flag=false;
 54         for(int &i=cur[u]; i!=-1; i=edge[i].next){
 55             int v=edge[i].v;
 56             if(edge[i].cap!=edge[i].flow && level[u]==level[v]+1){
 57                 flag=true;
 58                 pre[v]=u;
 59                 u=v;
 60                 //aug=(aug==-1?edge[i].cap:min(aug,edge[i].cap));
 61                 aug=min(aug,edge[i].cap-edge[i].flow);
 62                 if(v==vt){
 63                     flow+=aug;
 64                     for(u=pre[v]; v!=vs; v=u,u=pre[u]){
 65                         edge[cur[u]].flow+=aug;
 66                         edge[cur[u]^1].flow-=aug;
 67                     }
 68                     //aug=-1;
 69                     aug=INF;
 70                 }
 71                 break;
 72             }
 73         }
 74         if(flag) continue;
 75         int minlevel=NV;
 76         for(int i=head[u]; i!=-1; i=edge[i].next){
 77             int v=edge[i].v;
 78             if(edge[i].cap!=edge[i].flow && level[v]<minlevel){
 79                 minlevel=level[v];
 80                 cur[u]=i;
 81             }
 82         }
 83         if(--gap[level[u]]==0) break;
 84         level[u]=minlevel+1;
 85         gap[level[u]]++;
 86         u=pre[u];
 87     }
 88     return flow;
 89 }
 90 
 91 int cnt1,cnt2;
 92 bool vis1[MAXN],vis2[MAXN];
 93 void dfs1(int u){
 94     ++cnt1;
 95     for(int i=head[u]; i!=-1; i=edge[i].next){
 96         int v=edge[i].v;
 97         if(vis1[v] || edge[i].cap==edge[i].flow) continue;
 98         vis1[v]=1;
 99         dfs1(v);
100     }
101 }
102 void dfs2(int u){
103     ++cnt2;
104     for(int i=head[u]; i!=-1; i=edge[i].next){
105         int v=edge[i].v;
106         if(vis2[v] || edge[i^1].cap==edge[i^1].flow) continue;
107         vis2[v]=1;
108         dfs2(v);
109     }
110 }
111 int main(){
112     int m,a,b,c;
113     while(~scanf("%d%d%d%d",&NV,&m,&vs,&vt)&&(NV||m||vs||vt)){
114         NE=0;
115         memset(head,-1,sizeof(head));
116         while(m--){
117             scanf("%d%d%d",&a,&b,&c);
118             if(a==b) continue;
119             addEdge(a,b,c);
120             addEdge(b,a,c);
121         }
122         ISAP();
123 
124         cnt1=cnt2=0;
125         memset(vis1,0,sizeof(vis1));
126         memset(vis2,0,sizeof(vis2));
127         vis1[vs]=1; vis2[vt]=1;
128         dfs1(vs); dfs2(vt);
129 
130         if(cnt1+cnt2==NV) puts("UNIQUE");
131         else puts("AMBIGUOUS");
132     }
133     return 0;
134 }