nqueen_best_soln.cpp

#include <iostream>
using namespace std;
int board[100][100] = {0};
int n,ans=0,DONE;
int returnPosition(int n){
    int ans = 0;
    while(n>0){
        ans++;
        n = n>>1;
    }
    return ans-1;
}
void solve(int rowMask,int ld,int rd,int row){
    if(rowMask==DONE){
        ans++;
        for(int i = 0;i<n;++i){
            for(int j = 0;j<n;++j)
                cout<<board[i][j];
            cout<<"\n";
        }
        cout<<"\n";
        return;
    }
    int safe = DONE & (~(rowMask|ld|rd));
    while(safe){
        int p = safe & (-safe);
        int col = returnPosition(p);
        board[row][col] = 1;
        safe = safe - p;
        solve(rowMask|p,(ld|p)<<1,(rd|p)>>1,row+1);
        board[row][col] = 0;
    }
}


int main() {
    
    cin>>n;
    DONE = ((1<<n))-1;
    solve(0,0,0,0);
    cout<<ans;
}