Implement the n-queens problem
Do the followings: For n = 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15
1. Output the positions of queens for the n-queens problem.
2. Count the number of promising nodes before we find a solution of nqueen
3. Check the running time of each case of n-queens problem, draw a graph
with the running time, and do analysis the time complexity of the