Dear reader, welcome to the next problem in the Recursion & Backtracking section named 'Queens Combinations - 2d as 1d - Queen Chooses'.
If somehow you have landed on this problem directly, then I must tell you that the train is on an intermediate station.
The station of origin of our train was 'Queens Combinations - 2d As 2d - Box Chooses' and the previous station was 'Queens Combinations - 2d as 2d - Queen Chooses'. Please join the journey from the beginning to experience the full joy.
Also, there is a strong prerequisite for this set of problems on permutations & combinations in 2D grid, which is permutations & combinations in 1D.