POJ2112 Optimal Milking （网络流）（Dinic）

                                         Optimal Milking

Time Limit: 2000MS		Memory Limit: 30000K
Total Submissions: 16461		Accepted: 5911
Case Time Limit: 1000MS

Description

FJ has moved his K (1 <= K <= 30) milking machines out into the cow pastures among the C (1 <= C <= 200) cows. A set of paths of various lengths runs among the cows and the milking machines. The milking machine locations are named by ID numbers 1..K; the cow locations are named by ID numbers K+1..K+C.

Each milking point can "process" at most M (1 <= M <= 15) cows each day.

Write a program to find an assignment for each cow to some milking
machine so that the distance the furthest-walking cow travels is
minimized (and, of course, the milking machines are not overutilized).
At least one legal assignment is possible for all input data sets. Cows
can traverse several paths on the way to their milking machine.

Input

* Line 1: A single line with three space-separated integers: K, C, and M.

* Lines 2.. ...: Each of these K+C lines of K+C space-separated
integers describes the distances between pairs of various entities. The
input forms a symmetric matrix. Line 2 tells the distances from milking
machine 1 to each of the other entities; line 3 tells the distances
from machine 2 to each of the other entities, and so on. Distances of
entities directly connected by a path are positive integers no larger
than 200. Entities not directly connected by a path have a distance of
0. The distance from an entity to itself (i.e., all numbers on the
diagonal) is also given as 0. To keep the input lines of reasonable
length, when K+C > 15, a row is broken into successive lines of 15
numbers and a potentially shorter line to finish up a row. Each new row
begins on its own line.

Output

A single line with a single integer that is the minimum possible total distance for the furthest walking cow.

Sample Input

2 3 2
0 3 2 1 1
3 0 3 2 0
2 3 0 1 0
1 2 1 0 2
1 0 0 2 0

Sample Output

2

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <time.h>
#include <string>
#include <map>
#include <stack>
#include <vector>
#include <set>
#include <queue>
#define inf 0x3f3f3f3f
#define mod 10000
typedef long long ll;
using namespace std;
const int N=;
const int M=;
int power(int a,int b,int c){int ans=;while(b){if(b%==){ans=(ans*a)%c;b--;}b/=;a=a*a%c;}return ans;}
int dis[N][N];
int w[N][N];
bool sign[N][N];
bool used[N];
int k,c,n,m;
void Build_Graph(int min_max)
{
    memset(w,,sizeof(w));
    for(int i=;i<=k;i++)w[][i]=m;
    for(int i=k+;i<=n;i++)w[i][n+]=;
    for(int i=;i<=k;i++){
        for(int j=k+;j<=n;j++){
            if(dis[i][j]<=min_max) w[i][j]=;
        }
    }
}
bool BFS()
{
    memset(used,false,sizeof(used));memset(sign,,sizeof(sign));
    queue<int>q;
    q.push();used[]=true;
    while(!q.empty()){
        int t=q.front();q.pop();
        for(int i=;i<=n+;i++){
            if(!used[i]&&w[t][i]){
                q.push(i);
                used[i]=true;
                sign[t][i]=;
            }
        }
    }
    if(used[n+])return true;
    return false;
}
int DFS(int v,int sum)
{
    if(v==n+)return sum;
    int s=sum,t;
    for(int i=;i<=n+;i++){
        if(sign[v][i]){
            t=DFS(i,min(w[v][i],sum));
            w[v][i]-=t;
            w[i][v]+=t;
            sum-=t;
        }
    }
    return s-sum;
}
int main()
{
    scanf("%d%d%d",&k,&c,&m);
    n=k+c;
    for(int i=;i<=n;i++){
        for(int j=;j<=n;j++){
            scanf("%d",&dis[i][j]);
            if(!dis[i][j])dis[i][j]=inf;
        }
    }
    for(int k=;k<=n;k++){
        for(int i=;i<=n;i++){
            if(dis[i][k]!=inf){
                for(int j=;j<=n;j++){
                    dis[i][j]=min(dis[i][j],dis[i][k]+dis[k][j]);
                }
            }
        }
    }
    int l=,r=;
    while(l<r){
        int mid=(l+r)/;
        int ans=;
        Build_Graph(mid);
        while( BFS() )ans+=DFS(,inf);//Dinic求最大流
        if(ans>=c) r=mid;
        else l=mid+;
    }
    printf("%d\n",r);
    return ;
}