all_interval_series.py

# Copyright Microsoft Research 2016
# The following script finds sequences of length n-1 of
# integers 0,..,n-1 such that the difference of the n-1
# adjacent entries fall in the range 0,..,n-1
# This is known as the "The All-Interval Series Problem"
# See http://www.csplib.org/Problems/prob007/
from __future__ import print_function
from z3 import *
import time

set_option("sat.gc.burst", False)      # disable GC at every search. It is wasteful for these small queries.

def diff_at_j_is_i(xs, j, i):
    assert(0 <= j and j + 1 < len(xs))
    assert(1 <= i and i < len(xs))
    return Or([ And(xs[j][k], xs[j+1][k-i]) for k in range(i,len(xs))] + 
              [ And(xs[j][k], xs[j+1][k+i]) for k in range(0,len(xs)-i)])
    

def ais(n):
    xij = [ [ Bool("x_%d_%d" % (i,j)) for j in range(n)] for i in range(n) ]
    s = SolverFor("QF_FD")
# Optionally replace by (slower) default solver if using
# more then just finite domains (Booleans, Bit-vectors, enumeration types
# and bounded integers)
#   s = Solver() 
    for i in range(n):
        s.add(AtMost(xij[i] + [1]))
        s.add(Or(xij[i]))
    for j in range(n):
        xi = [ xij[i][j] for i in range(n) ]
        s.add(AtMost(xi + [1]))
        s.add(Or(xi))
    dji = [ [ diff_at_j_is_i(xij, j, i + 1) for i in range(n-1)] for j in range(n-1) ]
    for j in range(n-1):
        s.add(AtMost(dji[j] + [1]))
        s.add(Or(dji[j]))
    for i in range(n-1):
        dj = [dji[j][i] for j in range(n-1)]
        s.add(AtMost(dj + [1]))
        s.add(Or(dj))
    return s, xij

def process_model(s, xij, n):
    # x_ij integer i is at position j
    # d_ij difference between integer at position j, j+1 is i
    # sum_j d_ij = 1 i = 1,...,n-1
    # sum_j x_ij = 1
    # sum_i x_ij = 1
    m = s.model()
    block = []
    values = []
    for i in range(n):
        k = -1
        for j in range(n):
            if is_true(m.eval(xij[i][j])):
               assert(k == -1)
               block += [xij[i][j]]
               k = j
        values += [k]
    print(values)
    sys.stdout.flush()
    return block

def all_models(n):
    count = 0
    s, xij = ais(n)
    start = time.clock()
    while sat == s.check():
        block = process_model(s, xij, n)
        s.add(Not(And(block)))
        count += 1
    print(s.statistics())
    print(time.clock() - start)
    print(count)

set_option(verbose=1)  
all_models(12)