Add NQueens backtracking search implementation (TheAlgorithms#504)

Author: DaveAxiom

other/nqueens.py

@@ -0,0 +1,77 @@
+#! /usr/bin/python3
+importsys
+
+defnqueens(board_width):
+board= [0]
+current_row=0
+whileTrue:
+conflict=False
+
+forreview_indexinrange(0, current_row):
+left=board[review_index] - (current_row-review_index)
+right=board[review_index] + (current_row-review_index);
+if (board[current_row] ==board[review_index] or (left>=0andleft==board[current_row]) or (right<board_widthandright==board[current_row])):
+conflict=True;
+break
+
+if (current_row==0andconflict==False):
+board.append(0)
+current_row=1
+continue
+
+if (conflict==True):
+board[current_row] +=1
+
+if (current_row==0andboard[current_row] ==board_width):
+print("No solution exists for specificed board size.")
+returnNone
+
+whileTrue:
+if (board[current_row] ==board_width):
+board[current_row] =0
+if (current_row==0):
+print("No solution exists for specificed board size.")
+returnNone
+
+board.pop()
+current_row-=1
+board[current_row] +=1
+
+ifboard[current_row] !=board_width:
+break
+else:
+current_row+=1
+if (current_row==board_width):
+break
+
+board.append(0)
+returnboard
+
+defprint_board(board):
+if (board==None):
+return
+
+board_width=len(board)
+forrowinrange(board_width):
+line_print= []
+forcolumninrange(board_width):
+ifcolumn==board[row]:
+line_print.append("Q")
+else:
+line_print.append(".")
+print(line_print)
+
+
+if__name__=='__main__':
+default_width=8
+forarginsys.argv:
+if (arg.isdecimal() andint(arg) >3):
+default_width=int(arg)
+break
+
+if (default_width==8):
+print("Running algorithm with board size of 8. Specify an alternative Chess board size for N-Queens as a command line argument.")
+
+board=nqueens(default_width)
+print(board)
+print_board(board)