无源汇上下界可行流模版

来源：互联网发布：东莞金域名苑编辑：程序博客网时间：2024/05/16 16:55

http://acm.sgu.ru/problem.php?contest=0&problem=194

#include<cstdio>#include<iostream>#include<cstring>using namespace std;const int maxn = 210;const int maxm = 50000;const int INF = 0x3ffffff;struct Side{int to,next,c;}side[maxm*2];int node[maxn],dis[maxn],gap[maxn],start,end,cnt,top;void add_side(int u,int v,int c){side[top]=(Side){v,node[u],c};node[u]=top++;side[top]=(Side){u,node[v],0};node[v]=top++;}int get_flow(int u,int flow){if(u==end)return flow;int ans=0;for(int i=node[u];i!=-1;i=side[i].next){int v=side[i].to,c=side[i].c;if(dis[u]>dis[v]&&c){int f=get_flow(v,min(flow-ans,c));ans+=f;side[i].c-=f;side[i^1].c+=f;if(ans==flow)return flow;}}if(!(--gap[dis[u]]))dis[start]=cnt+2;gap[++dis[u]]++;return ans;}int up[maxm],low[maxm],du[maxn],id[maxm];int main(){int n,m;memset(node,-1,sizeof(node));scanf("%d%d",&n,&m);cnt=n+2;start=0;end=n+1;for(int i=0;i<m;i++){int u,v;scanf("%d%d%d%d",&u,&v,&low[i],&up[i]);du[v]+=low[i];du[u]-=low[i];add_side(u,v,up[i]-low[i]);id[i]=top-1;}int target=0;for(int i=1;i<=n;i++){if(du[i]>0){add_side(start,i,du[i]);target+=du[i];}else if(du[i]<0)add_side(i,end,-du[i]);}int ans=0;gap[0]=cnt;while(dis[start]<cnt)ans+=get_flow(start,INF);if(ans==target){printf("YES\n");for(int i=0;i<m;i++)printf("%d\n",low[i]+side[id[i]].c);}else printf("NO\n");}