ꦫꦣꦺꦤ꧀ꦄꦤ꧀ꦠꦱꦺꦤ

PATH: usr / lib64 / python2.7 / Demo / scripts

#! /usr/bin/env python

"""N queens problem.

The (well-known) problem is due to Niklaus Wirth.

This solution is inspired by Dijkstra (Structured Programming).  It is
a classic recursive backtracking approach.

"""

N = 8                                   # Default; command line overrides

class Queens:

def __init__(self, n=N):
        self.n = n
        self.reset()

def reset(self):
        n = self.n
        self.y = [None] * n             # Where is the queen in column x
        self.row = [0] * n              # Is row[y] safe?
        self.up = [0] * (2*n-1)         # Is upward diagonal[x-y] safe?
        self.down = [0] * (2*n-1)       # Is downward diagonal[x+y] safe?
        self.nfound = 0                 # Instrumentation

def solve(self, x=0):               # Recursive solver
        for y in range(self.n):
            if self.safe(x, y):
                self.place(x, y)
                if x+1 == self.n:
                    self.display()
                else:
                    self.solve(x+1)
                self.remove(x, y)

def safe(self, x, y):
        return not self.row[y] and not self.up[x-y] and not self.down[x+y]

def place(self, x, y):
        self.y[x] = y
        self.row[y] = 1
        self.up[x-y] = 1
        self.down[x+y] = 1

def remove(self, x, y):
        self.y[x] = None
        self.row[y] = 0
        self.up[x-y] = 0
        self.down[x+y] = 0

silent = 0                          # If true, count solutions only

def display(self):
        self.nfound = self.nfound + 1
        if self.silent:
            return
        print '+-' + '--'*self.n + '+'
        for y in range(self.n-1, -1, -1):
            print '|',
            for x in range(self.n):
                if self.y[x] == y:
                    print "Q",
                else:
                    print ".",
            print '|'
        print '+-' + '--'*self.n + '+'

def main():
    import sys
    silent = 0
    n = N
    if sys.argv[1:2] == ['-n']:
        silent = 1
        del sys.argv[1]
    if sys.argv[1:]:
        n = int(sys.argv[1])
    q = Queens(n)
    q.silent = silent
    q.solve()
    print "Found", q.nfound, "solutions."

if __name__ == "__main__":
    main()

[-] pi.pyo [edit]
[-] eqfix.pyo [edit]
[-] makedir.pyc [edit]
[-] queens.py [edit]
[-] queens.pyo [edit]
[-] pp.py [edit]
[-] unbirthday.py [edit]
[-] update.pyo [edit]
[-] fact.pyc [edit]
[-] pp.pyc [edit]
[-] primes.pyo [edit]
[-] markov.pyc [edit]
[-] eqfix.py [edit]
[-] mboxconvert.pyo [edit]
[+] ..
[-] newslist.py [edit]
[-] README [edit]
[-] newslist.pyc [edit]
[-] markov.py [edit]
[-] newslist.pyo [edit]
[-] pi.pyc [edit]
[-] morse.py [edit]
[-] beer.pyc [edit]
[-] newslist.doc [edit]
[-] beer.pyo [edit]
[-] primes.py [edit]
[-] pi.py [edit]
[-] find-uname.pyc [edit]
[-] makedir.pyo [edit]
[-] eqfix.pyc [edit]
[-] mboxconvert.pyc [edit]
[-] fact.py [edit]
[-] unbirthday.pyc [edit]
[-] script.pyo [edit]
[-] primes.pyc [edit]
[-] find-uname.pyo [edit]
[-] lpwatch.pyo [edit]
[-] morse.pyo [edit]
[-] fact.pyo [edit]
[-] morse.pyc [edit]
[-] from.py [edit]
[-] from.pyo [edit]
[-] makedir.py [edit]
[-] update.py [edit]
[-] lpwatch.pyc [edit]
[-] find-uname.py [edit]
[-] script.pyc [edit]
[-] queens.pyc [edit]
[-] from.pyc [edit]
[-] unbirthday.pyo [edit]
[-] lpwatch.py [edit]
[-] beer.py [edit]
[-] markov.pyo [edit]
[-] update.pyc [edit]
[-] pp.pyo [edit]
[-] mboxconvert.py [edit]
[-] script.py [edit]