AI-N Queen Problem(dfs)

#include <cstdio>//the biggest N of this dfs method is 29(4s)
#include <iostream>
#include <algorithm>
using namespace std;
int col[50];//col[row] seems the col of queen in the row
int n;
bool check(int r,int c)
{
int i;
for(i=1;i<r;i++)//make sure all the previous points are not conflict with the current one
if(c==col[i]||(r-i)==abs(c-col[i]))//the cols and diagonal lines
return false;
return true;
}

bool dfs(int r)
{
col[r]++;
col[r+1]=0;//when a queen is finding her place,next queen must not be set.
if(check(r,col[r])&&col[r]<=n)//if the queen find her place
{
if(r==n)//if all queens have been set
{
int w;
for(w=1;w<=n;w++)
printf("(%d,%d) ",w,col[w]);
cout<<endl;
return true;//return true to the upper level,telling them the mission has been finished.
}
int j;
for(j=1;j<=n;j++)
if(dfs(r+1))
return true;
}
return false;
}
int main()
{
cin>>n;
int i;
for(i=1;i<=n;i++)
col[i]=0;//queens haven't been set yet
for(i=1;i<=n;i++)
if(dfs(1))
return 0;//exit when finding the first path.
}