Queen eight, backtracking and Recursion

The eight-queen code of the python statement, from the basic Python tutorial, is short and can print 92 results at a time compared with other languages. At the same time, it can be extended to the ten queen problem after the nine emperors.

Problem: On an 8x8 board, each row is placed with a queen flag, and they do not conflict. Conflict definition: the same column cannot have two queens, and each diagonal line cannot have two queens. Of course, neither can the three queens, nor can the four be. I should be able to understand it with IQ.

　　

Solution: backtracking and Recursion

 1 import random 2  3 def conflict(state,col): 4     row=len(state) 5     for i in range(row): 6         if abs(state[i]-col) in (0,row-i): 7             return True 8     return False 9 10 11     12 def queens(num=8,state=()):13     for pos in range(num):14         if not conflict(state, pos):15             if len(state)==num-1:16                 yield(pos,)17             else:18                 for result in queens(num, state+(pos,)):19                     yield (pos,)+result20 21 22 23 def queenprint(solution):24     def line(pos,length=len(solution)):25         return ‘. ‘*(pos)+‘X ‘+‘. ‘*(length-pos-1)26     for pos in solution:27         print line(pos)28         29 30 for solution in list(queens(8)):31     print solution32 print ‘  total number is ‘+str(len(list(queens())))33 print ‘  one of the range is:\n‘34 queenprint(random.choice(list(queens())))

 

Introduction:

1. Backtracking

2. Recursion

To be continued

 

Queen eight, backtracking and Recursion