POJ-3189 Steady Cow Assignment

网络流+二分+枚举区间

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<queue>
using namespace std;
typedef long long ll;
const int N=1020+10;
const int M=5e4+10;
const int INF=0x7f7f7f7f;
struct Edge
{
    int to,nxt,cap,flow;
}edge[M];
int tot,first[N];
void addedge(int u,int v,int w,int rw=0)
{
    edge[tot].to=v;edge[tot].cap=w;edge[tot].flow=0;
    edge[tot].nxt=first[u];first[u]=tot++;
    edge[tot].to=u;edge[tot].cap=rw;edge[tot].flow=0;
    edge[tot].nxt=first[v];first[v]=tot++;
}
void init()
{
    tot=0;
    memset(first,-1,sizeof(first));
}

int gap[N],dep[N],cur[N];
int Q[N],S[N];
void bfs(int s)
{
    memset(gap,0,sizeof(gap));
    memset(dep,-1,sizeof(dep));
    int q0=0,q1=0;
    Q[q1++]=s;
    dep[s]=0;
    gap[0]=1;
    while(q0<q1)
    {
        int u=Q[q0++];
        for(int i=first[u];i!=-1;i=edge[i].nxt)
        {
            int v=edge[i].to;
            if(dep[v]!=-1) continue;
            Q[q1++]=v;
            dep[v]=dep[u]+1;
            gap[dep[v]]++;
        }
    }
}
int sap(int s,int t,int n)
{
    int ans=0;
    bfs(t);
    memcpy(cur,first,sizeof(first));
    int top=0;
    int u=s;
    while(dep[s]<n)
    {
        if(u==t)
        {
            int Min=INF;
            int inser;
            for(int i=0;i<top;i++)
                if(Min>edge[S[i]].cap-edge[S[i]].flow)
                {
                    Min=edge[S[i]].cap-edge[S[i]].flow; 
                    inser=i;
                }
            for(int i=0;i<top;i++)
            {
                edge[S[i]].flow+=Min;
                edge[S[i]^1].flow-=Min;
            }
            ans+=Min;
            top=inser;
            u=edge[S[top]^1].to;
        }
        bool flag=false;
        int v;
        for(int i=cur[u];i!=-1;i=edge[i].nxt)
        {
            v=edge[i].to;
            if(edge[i].cap-edge[i].flow&&dep[v]+1==dep[u])
            {
                flag=true;
                cur[u]=S[top++]=i;
                break;
            }
        }
        if(flag)
        {
            u=v;
            continue;
        }
        gap[dep[u]]--;
        if(!gap[dep[u]]) return ans;
        int Min=n;
        for(int i=first[u];i!=-1;i=edge[i].nxt)
            if(edge[i].cap-edge[i].flow&&Min>dep[edge[i].to])
            {
                Min=dep[edge[i].to];
                cur[u]=i;
            }
        dep[u]=Min+1;
        gap[dep[u]]++;
        if(u!=s) u=edge[S[--top]^1].to;
    }
    return ans;
}
int g[N][N];
int num[N];
int main()
{
    int n,m,a;
    while(~scanf("%d%d",&n,&m))
    {
        int s=n+m,t=s+1;
        for(int i=0;i<n;i++)
            for(int j=0;j<m;j++)
            {
                scanf("%d",&a);
                g[i][a+n-1]=j+1;
            }
        for(int i=n;i<s;i++)
            scanf("%d",&num[i]);
        int ans=m,l=1,r=m;
        while(l<=r)
        {
            int mid=(l+r)>>1;
            bool flag=false;
            for(int k=1;k+mid-1<=m;k++)
            {
                init();
                for(int i=0;i<n;i++)
                    addedge(s,i,1);
                for(int i=n;i<s;i++)
                    addedge(i,t,num[i]);
                for(int i=0;i<n;i++)
                    for(int j=n;j<s;j++)
                        if(g[i][j]>=k&&g[i][j]<=k+mid-1)
                            addedge(i,j,1);
                int num=sap(s,t,t+1);
                if(num==n)
                {
                    flag=true;
                    break;
                }
            }
            if(!flag)
            {
                l=mid+1;
            }
            else
            {
                ans=mid;
                r=mid-1;
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}