poj 2112 (最大流+二分)
题意:有k台挤奶机,c头奶牛,给出这k+c个实体间的距离,求出每头奶牛都到一台挤奶机去,怎么分配使奶牛走的最大距离最小。
用二分枚举最大距离,,,,
#include<stdio.h> #include<string.h> #define N 500 #define inf 0x3fffffff int map[N][N],dis[N],gap[N],head[N],num,n,m,D,start,end,ans; struct edge { int st,ed,flow,next; }E[N*40]; void addedge(int x,int y,int w) { E[num].st=x;E[num].ed=y;E[num].flow=w;E[num].next=head[x];head[x]=num++; E[num].st=y;E[num].ed=x;E[num].flow=0;E[num].next=head[y];head[y]=num++; } int dfs(int u,int minflow) { if(u==end)return minflow; int i,v,f,min_dis=ans-1,flow=0; for(i=head[u];i!=-1;i=E[i].next) { if(E[i].flow>0) { v=E[i].ed; if(dis[v]+1==dis[u]) { f=dfs(v,E[i].flow>minflow-flow?minflow-flow:E[i].flow); E[i].flow-=f; E[i^1].flow+=f; flow+=f; if(flow==minflow)break; if(dis[start]>=ans)return flow; } min_dis=min_dis>dis[v]?dis[v]:min_dis; } } if(flow==0) { if(--gap[dis[u]]==0) dis[start]=ans; dis[u]=min_dis+1; gap[dis[u]]++; } return flow; } int isap() { int maxflow=0; memset(dis,0,sizeof(dis)); memset(gap,0,sizeof(gap)); gap[0]=ans; while(dis[start]<ans) maxflow+=dfs(start,inf); return maxflow; } void makemap(int DD) { int i,j; memset(head,-1,sizeof(head)); num=0; for(i=1;i<=m;i++) addedge(start,i+n,1); for(i=1;i<=n;i++) addedge(i,end,D); for(i=n+1;i<=n+m;i++) for(j=1;j<=n;j++) { if(map[i][j]<=DD&&map[i][j]!=0) addedge(i,j,1); } } int main() { int i,j,k,left,right,mid; while(scanf("%d%d%d",&n,&m,&D)!=-1) { left=0;right=0;start=0;end=n+m+1;ans=end+1; memset(map,0,sizeof(map)); for(i=1;i<=n+m;i++) for(j=1;j<=n+m;j++) scanf("%d",&map[i][j]); for(k=1;k<=n+m;k++) { for(i=1;i<=n+m;i++) { if(map[i][k]==0)continue;//0表示不连通 for(j=1;j<=n+m;j++) { if(map[k][j]==0||i==j)continue; if(map[i][j]==0||map[i][j]>map[i][k]+map[k][j]) map[i][j]=map[i][k]+map[k][j]; if(right<map[i][j]) right=map[i][j]; } } } while(left<right) { mid=(left+right)/2; makemap(mid); int sum=isap(); if(sum==m) right=mid; else left=mid+1; } printf("%d\n",right); } return 0; }