标签:class false pre flow space clu lap bsp ext
正反两遍spfa,判断某条边是否是在最短路上,如果是的话就建边,跑最大流
1 #include<cstdio> 2 #include<queue> 3 #include<cstring> 4 #include<algorithm> 5 using namespace std; 6 #define maxn 250000 7 #define inf 0x3f3f3f3f 8 int n,m,src,dec,ans,cur[maxn],d[maxn],ansx,y,z,num,front2[maxn*2]; 9 int lev[maxn],front[maxn*2],head,tail,que[maxn*2],tot=1,dis[maxn],dis1[maxn]; 10 bool vis[maxn]; 11 struct node{ 12 int to,next,cap; 13 }e[maxn*2]; 14 15 struct Edge{ 16 int u,v,next,w,d; 17 }edge[maxn*2],edge2[maxn*2]; 18 19 inline void add(int u,int v,int w) 20 { 21 e[++tot].to=v; e[tot].next=front[u]; e[tot].cap=w; front[u]=tot; 22 e[++tot].to=u; e[tot].next=front[v]; e[tot].cap=0; front[v]=tot; 23 } 24 25 void ins(int u,int v,int w,int d) 26 { 27 edge[++num].v=v; 28 edge[num].w=w; 29 edge[num].u=u; 30 edge[num].next=front2[u]; 31 edge[num].d=d; 32 front2[u]=num; 33 } 34 35 char ch; 36 inline void read(int &now) 37 { 38 ch=getchar(); now=0; 39 while(ch>‘9‘||ch<‘0‘) ch=getchar(); 40 while(ch>=‘0‘&&ch<=‘9‘) now=now*10+ch-‘0‘,ch=getchar(); 41 } 42 43 bool bfs() 44 { 45 for(int i=src;i<=dec;i++) lev[i]=-1,cur[i]=front[i]; 46 head=tail=0; 47 que[tail++]=src; lev[src]=0; 48 while(head<tail) 49 { 50 for(int i=front[que[head]];i;i=e[i].next) 51 if(e[i].cap>0&&lev[e[i].to]==-1) 52 { 53 lev[e[i].to]=lev[que[head]]+1; 54 que[tail++]=e[i].to; 55 if(e[i].to==dec) return true; 56 } 57 head++; 58 } 59 return false; 60 } 61 62 void spfa(int s) 63 { 64 queue<int>q; 65 for(int i=1;i<=n;i++) dis[i]=inf; 66 memset(vis,false,sizeof(false)); 67 vis[s]=1; dis[s]=0; 68 q.push(s); 69 while(!q.empty()) 70 { 71 int cur=q.front(); q.pop(); 72 for(int i=front2[cur];i;i=edge[i].next) 73 { 74 if(dis[edge[i].v]>dis[cur]+edge[i].w) 75 { 76 dis[edge[i].v]=dis[cur]+edge[i].w; 77 if(!vis[edge[i].v]) 78 { 79 vis[edge[i].v]=1; 80 q.push(edge[i].v); 81 } 82 } 83 } 84 vis[cur]=false; 85 } 86 } 87 88 int dinic(int u,int flow) 89 { 90 if(u==dec) return flow; 91 int res=0,delta; 92 for(int i=cur[u];i;i=e[i].next) 93 { 94 if(e[i].cap>0&&lev[e[i].to]>lev[u]) 95 { 96 delta=dinic(e[i].to,min(e[i].cap,flow-res)); 97 if(delta) 98 { 99 e[i].cap-=delta; e[i^1].cap+=delta; 100 res+=delta; if(res==flow) break; 101 } 102 } 103 } 104 if(res!=flow) lev[u]=-1; 105 return res; 106 } 107 108 int main() 109 { 110 read(n); read(m); 111 for(int i=1;i<=m;i++) 112 { 113 int u,v,w,d; 114 read(u); read(v); read(w); read(d); 115 edge2[i].u=u; edge2[i].v=v; edge2[i].w=w; edge2[i].d=d; 116 ins(u,v,w,d); 117 ins(v,u,w,d); 118 } 119 src=1; dec=n; 120 spfa(src); 121 printf("%d\n",dis[n]); 122 for(int i=1;i<=n;i++) dis1[i]=dis[i]; 123 spfa(dec); 124 for(int i=1;i<=m;i++) 125 { 126 if(dis1[edge2[i].u]<dis1[edge2[i].v]) 127 { 128 if(edge2[i].w+dis1[edge2[i].u]+dis[edge2[i].v]==dis1[n]) 129 add(edge2[i].u,edge2[i].v,edge2[i].d); 130 } 131 else{ 132 if(edge2[i].w+dis1[edge2[i].v]+dis[edge2[i].u]==dis1[n]) 133 add(edge2[i].v,edge2[i].u,edge2[i].d); 134 } 135 } 136 while(bfs()) 137 ans+=dinic(src,inf); 138 printf("%d\n",ans); 139 return 0; 140 }
标签:class false pre flow space clu lap bsp ext
原文地址:http://www.cnblogs.com/chen74123/p/7491549.html