What is N-Queen problem?

The N Queen is the problem of placing N chess queens on an N×N chessboard so that no two queens attack each other.

For example, the following is a solution for the 4 Queen problem.

The expected output is in the form of a matrix that has ‘Q‘s for the blocks where queens are placed and the empty spaces are represented by ‘.’ . For example, the following is the output matrix for the above 4-Queen solution.

. Q . .
. . . Q 
Q . . .
. . Q . 

We have discussed Knight’s tour and Rat in a Maze problem earlier as examples of Backtracking problems. Let us discuss N Queen as another example problem that can be solved using backtracking.