POJ 3189 Steady Cow Assignment

枚举+最大流

#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;

int g[1005][25];
int val[25];
int N,B;

const int maxn = 1000 + 50;
const int INF = 0x7FFFFFFF;
struct Edge
{
    int from, to, cap, flow;
    Edge(int u, int v, int c, int f) :from(u), to(v), cap(c), flow(f) {}
};
vector<Edge>edges;
vector<int>G[maxn];
bool vis[maxn];
int d[maxn];
int cur[maxn];
int n, m, s, t;

void init()
{
    for (int i = 0; i < maxn; i++) G[i].clear();
    edges.clear();
}
void AddEdge(int from, int to, int cap)
{
    edges.push_back(Edge(from, to, cap, 0));
    edges.push_back(Edge(to, from, 0, 0));
    int w = edges.size();
    G[from].push_back(w - 2);
    G[to].push_back(w - 1);
}
bool BFS()
{
    memset(vis, 0, sizeof(vis));
    queue<int>Q;
    Q.push(s);
    d[s] = 0;
    vis[s] = 1;
    while (!Q.empty())
    {
        int x = Q.front();
        Q.pop();
        for (int i = 0; i<G[x].size(); i++)
        {
            Edge e = edges[G[x][i]];
            if (!vis[e.to] && e.cap>e.flow)
            {
                vis[e.to] = 1;
                d[e.to] = d[x] + 1;
                Q.push(e.to);
            }
        }
    }
    return vis[t];
}
int DFS(int x, int a)
{
    if (x == t || a == 0)
        return a;
    int flow = 0, f;
    for (int &i = cur[x]; i<G[x].size(); i++)
    {
        Edge e = edges[G[x][i]];
        if (d[x]+1 == d[e.to]&&(f=DFS(e.to,min(a,e.cap-e.flow)))>0)
        {
            edges[G[x][i]].flow+=f;
            edges[G[x][i] ^ 1].flow-=f;
            flow+=f;
            a-=f;
            if(a==0) break;
        }
    }
    if(!flow) d[x] = -1;
    return flow;
}
int dinic(int s, int t)
{
    int flow = 0;
    while (BFS())
    {
        memset(cur, 0, sizeof(cur));
        flow += DFS(s, INF);
    }
    return flow;
}

int main()
{
    while(~scanf("%d%d",&N,&B))
    {
        int ans=INF;
        for(int i=1; i<=N; i++)
            for(int j=1; j<=B; j++)
                scanf("%d",&g[i][j]);
        for(int i=1; i<=B; i++) scanf("%d",&val[i]);
        s=0,t=N+B+1;
        int len;
        for(int i=1; i<=B; i++)
        {
            for(int j=i; j<=B; j++)
            {
                len=j-i+1;
                init();
                for(int ii=1; ii<=N; ii++) AddEdge(s,ii,1);
                for(int c=1; c<=N; c++)
                    for(int r=i; r<=j; r++)
                        AddEdge(c,g[c][r]+N,1);
                for(int ii=1; ii<=B; ii++) AddEdge(ii+N,t,val[ii]);
                if(dinic(s, t)==N)
                {
                    if(len<ans) ans=len;
                    break;
                }
            }

        }
        printf("%d
",ans);
    }
    return 0;
}