bzoj1070: [SCOI2007]修车

#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
const int maxn = 10000 + 10;
const int maxm = 1000000 + 10;
const int inf = 0x3f3f3f3f;

int g[maxn],v[maxm],next[maxm],f[maxm],c[maxm],eid;
int id[10][maxn],cnt[10],vid;
int dist[maxn],pre[maxn];
int q[maxm],l,r;
bool inque[maxn];
int t[110][20];
int m,n,res,S,T;

void addedge(int a,int b,int C) {
    v[eid]=b; f[eid]=1; c[eid]=C; next[eid]=g[a]; g[a]=eid++;
    v[eid]=a; f[eid]=0; c[eid]=-C; next[eid]=g[b]; g[b]=eid++;
}

void build() {
    scanf("%d%d",&m,&n);
    for(int i=1;i<=n;i++) 
    for(int j=1;j<=m;j++)
        scanf("%d",&t[i][j]);
    memset(g,-1,sizeof(g));
    S=0; T=maxn-1; vid=n;
    for(int i=1;i<=n;i++) addedge(S,i,0);
    for(int p=1;p<=m;p++) {
        id[p][++cnt[p]]=++vid;
        addedge(vid,T,0);
        for(int i=1;i<=n;i++) 
            addedge(i,vid,t[i][p]);        
    }
}

void augment() {
    for(int i=T;i!=S;i=v[pre[i]^1]) {
        f[pre[i]]--;
        f[pre[i]^1]++;
    }
    res+=dist[T];
}

int SPFA() {
    memset(dist,0x3f,sizeof(dist));
    memset(pre,-1,sizeof(pre));
    l=r=0;
    dist[S]=0;
    inque[q[r++]=S]=1;
    int u;
    while(l<r) {
        inque[u=q[l++]]=0;
        for(int i=g[u];~i;i=next[i]) 
        if(f[i] && dist[v[i]]>dist[u]+c[i]) {
            dist[v[i]]=c[i]+dist[u];
            pre[v[i]]=i;
            if(!inque[v[i]]) inque[q[r++]=v[i]]=1;
        }
    }
    augment();
    return v[pre[T]^1];
}

bool alter(int x) {
    int p;
    for(p=1;p<=m;p++) if(id[p][cnt[p]]==x) break;
    id[p][++cnt[p]]=++vid;
    addedge(vid,T,0);
    for(int i=1;i<=n;i++) 
        addedge(i,vid,t[i][p]*cnt[p]);    
}

void solve() {
    for(int i=1;i<=n;i++) alter(SPFA());
    printf("%.2lf\n",1.0*res/n);
}

int main() {
    build();
    solve();
    return 0;    
}