void dfs(int row,const int n,int *col,int*xy,int*yx,int *ans){
    *ans = *ans + (row == n);
    for(int i = 0; i < n && row < n;i++)
        if(!col[i] && !xy[n + row - i] && !yx[row + i])
            dfs(row + (col[i] = xy[n + row - i] = yx[ row + i] = 1),n,col,xy,yx,ans),
            col[i] = xy[n + row - i] = yx[ row + i] = 0;
}
int totalNQueens(int n) {
    int col[64]={0},xy[64]={0},yx[64]={0},ans=0;
    dfs(0,n,col,xy,yx,&ans);
    return ans;
}