形象生动的最小割。。
1 #include
2 #include
3 #include
4 #include
5 using namespace std;
6 #define INF (1<<30)
7 #define MAXN 2222
8 #define MAXM 888888
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
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] 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] 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 int main(){ 91 int n,m,a,b,c; 92 scanf("%d%d",&n,&m); 93 vs=0; vt=n+1; NV=vt+1; 94 memset(head,-1,sizeof(head)); 95 for(int i=1; i<=n; ++i){ 96 scanf("%d%d",&a,&b); 97 addEdge(vs,i,a); 98 addEdge(i,vt,b); 99 } 100 while(m--){ 101 scanf("%d%d%d",&a,&b,&c); 102 addEdge(a,b,c); 103 addEdge(b,a,c); 104 } 105 printf("%d",ISAP()); 106 return 0; 107 } 文章链接
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