uva11214 Guarding the Chessboard

http://acm.hust.edu.cn/vjudge/contest/view.action?cid=100945#problem/A

#include
      
       #define REP(i,a,b) for(int i=a;i<=b;i++)#define MS0(a) memset(a,0,sizeof(a))#define PII pair
       
        using namespace std;typedef long long ll;const int maxn=1000100;const int INF=(1<<29);int n,m;char ch[12][12];int id[12][12];PII X[maxn];int cnt;bool put[12][12];vector
        
          Put(int x,int y){    vector
         
           res;    REP(i,1,n){        if(put[i][y]==0){            put[i][y]=1;            res.push_back({i,y});        }    }    REP(i,1,m){        if(put[x][i]==0){            put[x][i]=1;            res.push_back({x,i});        }    }    REP(i,1,n){        int j=x+y-i;        if(j>=1&&j<=m&&put[i][j]==0){            put[i][j]=1;res.push_back({i,j});        }        j=i-(x-y);        if(j>=1&&j<=m&&put[i][j]==0){            put[i][j]=1;res.push_back({i,j});        }    }    return res;}void Put_pre(vector
          
            v){    for(int i=0;i
           
             v=Put(x,i); if(dfs(x,i,cur+1,maxd)) return 1; Put_pre(v); } REP(i,x+1,n){ REP(j,1,m){ vector
            
              v=Put(i,j); if(dfs(i,j,cur+1,maxd)) return 1; Put_pre(v); } } return 0;}int main(){ freopen("in.txt","r",stdin); int casen=1; while(cin>>n,n){ cin>>m; cnt=0;MS0(id); REP(i,1,n){ REP(j,1,m){ cin>>ch[i][j]; if(ch[i][j]=='X') id[i][j]=++cnt,X[cnt]={i,j}; } } int ans=INF; for(int i=0;;i++){ //cout<
             <