hdu 1565 方格取数

最大点权独立集->最小点权覆盖集->最小割->最大流~

果然细节最多的还是网络流~~~

#include<iostream>
#include<queue>
#include<vector>
#include<iomanip>
#include<string>
#include<algorithm>
using namespace std;

const int inf = 0x3f3f3f3f;
const int dir[4][2] = {{0,1},{0,-1},{-1,0},{1,0}};
const int maxn = 55;
const int maxc = 555;
vector<int> g[maxc];
int f[maxc][maxc];
int c[maxc][maxc];
bool you[maxc][maxc];
int cen[maxc];
int n,total;
int a[maxn][maxn];
queue<int>q;

int dx(int index)
{
    return (index-1)/n + 1;
}
int dy(int index)
{
    return (index % n) ? index % n : n;
}
int num(int x,int y)
{
    return (x-1)*n+y;
}
bool yes(int x,int y)
{
    if(x>=1 && x<=n && y>=1 && y<=n)
    {
        return true;
    }
    return false;
}
void init()
{
    memset(you,false,sizeof(you));
    memset(f,0,sizeof(f));
    memset(c,0,sizeof(c));
    for(int i=0;i<=n*n+1;i++)
    {
        g[i].clear();
    }
    return ;
}

bool bfs()
{
    while(!q.empty())
    {
        q.pop();
    }
    memset(cen,-1,sizeof(cen));
    q.push(0);
    cen[0]=0;
    int now,to;
    while(!q.empty())
    {
        now = q.front();
        q.pop();
        for(int i=0;i<g[now].size();i++)
        {
            to = g[now][i];
            if(! you[now][to] || cen[to]!=-1 )
            {
                continue;
            }
            cen[to]=cen[now] + 1;
            q.push(to);
        }
    }
    if(cen[n*n+1] == -1)
    {
        return false;
    }
    else
    {
        return true;
    }
}

int dfs(int now = 0,int flow = inf)
{
    if(cen[now] == cen[n*n+1])
    {
        if(now == n*n+1)
        {
            return flow;
        }
        else
        {
            return 0;
        }
    }
    int temp,sum;
    sum=0;
    for(int i=0;i<g[now].size();i++)
    {
        if(!you[now][g[now][i]] || cen[g[now][i]] - cen[now] != 1 )
        {
            continue;
        }
        temp = dfs(g[now][i] , min ( flow , c[now][g[now][i]] - f[now][g[now][i]] ) );
        f[now][g[now][i]] += temp;
        f[g[now][i]][now] -= temp;
        sum += temp;
        flow -= temp;
        if(f[now][g[now][i]] == c[now][g[now][i]] )
        {
            you[now][g[now][i]] = false;
        }
        you[g[now][i]][now] = true;
    }
    return sum;
}

int dinic()
{
    int ans = 0;
    while( bfs() )
    {
        ans += dfs();
    }
    return ans;
}

int main()
{
    while(cin>>n)
    {
        init();
        total=0;
        for(int i=1;i<=n;i++)
        {
            for(int j=1;j<=n;j++)
            {
                cin>>a[i][j];
                total += a[i][j];
            }
        }
        int tx,ty;
        for(int i=1;i<=n*n;i++)
        {
            if( (dx(i)+dy(i))%2 == 0 )
            {
                you[0][i] = true;
                c[0][i] = a[dx(i)][dy(i)];
                g[0].push_back(i);
                g[i].push_back(0);
                for(int j=0;j<4;j++)
                {
                    tx = dx(i) + dir[j][0];
                    ty = dy(i) + dir[j][1];
                    if(!yes(tx,ty)) continue;
                    c[i][num(tx,ty)]=inf;
                    you[i][num(tx,ty)] = true;
                    g[i].push_back(num(tx,ty));
                    g[num(tx,ty)].push_back(i);
                }
            }
            else
            {
                c[i][n*n + 1] = a[dx(i)][dy(i)];
                you[i][n*n + 1] =true;
                g[n*n + 1].push_back(i);
                g[i].push_back(n*n+1);
            }

        }
        cout<<total - dinic()<<endl;
    }
    return 0;
}