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题意：同一行或者列的炮台会被射到，求一个位置设炮台使得其炸掉的炮台最多

ac代码：

#include <bits/stdc++.h>
#include <stdio.h>
#define ff(i,x,y)for(int i=x;i<y+1;i++)
#define fs(i,x,y)for(int i=x;i>y-1;i--)
#define all(x) x.begin(),x.end()
#define Ins(x) inserter(x,x.begin())
using namespace std;
int n,m,p[4010],viscol[2010],visrow[2010],mes[4010],dx[4]={0,0,1,-1},dy[4]={1,-1,0,0};
char mp[2010][2010];
vector<int>col[2010],row[2010];
typedef pair<int,int> pii;
bool ppan(int x,int y)
{
    if(x>=1&&x<=n&&y>=1&&y<=m)
    return true;
    return false;
}
void bfs(int x,int y)
{
    queue<pii>hu;
    pii now(x,y);
    hu.push(now);
    int sum=(col[now.second].size()+row[now.first].size());
    sum--;
    while(!hu.empty())
    {
        now=hu.front();
        hu.pop();
        int ne;
        ff(i,0,col[now.second].size()-1)
        {
            ne=col[now.second][i];
            if(!visrow[ne])
            {
                visrow[ne]=1;
                p[ne]=p[x];
                ff(j,0,row[ne].size()-1)
                if(!viscol[row[ne][j]])
                sum++;
                hu.push(pii(ne,now.second));
            }
        }
        ff(i,0,row[now.first].size()-1)
        {
            ne=row[now.first][i];
            if(!viscol[ne])
            {
                viscol[ne]=1;
                p[ne+n]=p[x];
                 ff(j,0,col[ne].size()-1)
                if(!visrow[col[ne][j]])
                sum++;
                hu.push(pii(now.first,ne));
            }
        }
    }
    mes[p[x]]=sum;
}
int main()
{
    scanf("%d%d",&n,&m);
    ff(i,1,n)
    {
        p[i]=i;
        scanf("%s",mp[i]+1);
        ff(j,1,m)
        {
            p[j+n]=j+n;
            if(mp[i][j]=='+')
            {
                col[j].push_back(i);
                row[i].push_back(j);
            }
        }
    }
    int res=0,posx,posy,hupan=0;
    ff(i,1,n)
    {
        ff(j,1,m)
        {
            if(!viscol[j]&&!visrow[i]&&mp[i][j]=='+')
            {
                viscol[j]=1;
                visrow[i]=1;
                p[j+n]=p[i];
                bfs(i,j);
            }
        }
    }
    ff(i,1,n)
    {
        ff(j,1,m)
        {
            int nownum=0;
            if(mp[i][j]=='.')
            {
                if(p[i]==p[j+n])
                nownum=mes[p[i]];
                else
                nownum=mes[p[i]]+mes[p[j+n]];
            }
            if(nownum>res)
            {
                hupan=1;
                res=nownum;
                posx=i;
                posy=j;
            }
        }
    }
    if(hupan)
    printf("%d\n%d %d",res,posx,posy);
    else
    printf("0");
    return 0;
}

关键：visrow viscol 去标记行列，标记每一个点会超时