Backtracking

Algorithm

1) Start in the leftmost column
2) If all queens are placed
    return true
3) Try all rows in the current column.  Do following
   for every tried row.
    a) If the queen can be placed safely in this row
       then mark this as part of the 
       solution and recursively check if placing  
       queen here leads to a solution.
    b) If placing queen in leads to a
       solution then return true.
    c) If placing queen doesn't lead to a solution 
       then unmark this
       and go to step (a) to try other rows.
3) If all rows have been tried and nothing worked, 
   return false to trigger backtracking.
 
 
 
 (https://www.geeksforgeeks.org/printing-solutions-n-queen-problem/)