Question

   def solve(numLegs, numHeads):
        for numSpiders in range(0, numHeads + 1):
            for numChicks in range(0, numHeads - numSpiders + 1):
                numPigs = numHeads - numChicks - numSpiders
                totLegs = 4*numPigs + 2*numChicks + 6*numSpiders 
                if totLegs == numLegs:
                    return [numPigs, numChicks, numSpiders]
        return [None, None, None]

    def barnYard(heads, legs):
        pigs, chickens, spiders = solve(legs, heads)
        if pigs == None:
            print "There is no solution."
        else:
            print 'Number of pigs: ', pigs
            print 'Number of Chickens: ', chickens
            print 'Number of Spider: ', spiders

    barnYard(20,56) # 8 pigs - 12 chickens
    barnYard(21,62) # 10 pig - 11 chickens

20 heads and 56 legs returns 8 pigs and 12 chickens, so I made it 21 and 62 to add a spider, but it still returns pigs and chickens, whats wrong in the code?

Thanks!

Answer 1

Your code is correct – in the first iteration of the outermost for loop, numChicks is 0. Since solve returns as soon as it finds a valid match, another possible valid match won’t be attempted.

You could change the return statement into a yield statement and iterate over solve‘s results to get all possible combinations.

For instance:

def solve(numLegs, numHeads):
     for numBees in range(0, numHeads + 1):
             for numChicks in range(0, numHeads - numBees + 1):
                     numPigs = numHeads - numChicks - numBees
                     totLegs = 4*numPigs + 2*numChicks + 6*numBees 
                     if totLegs == numLegs:
                             yield [numPigs, numChicks, numBees]

def barnYard(heads, legs):
    for pigs, chickens, bees in solve(legs, heads):
             print 'Number of pigs: ', pigs
             print 'Number of chickens: ', chickens
             print 'Number of bees: ', bees

barnYard(20,56)

will output:

Number of pigs:  8
Number of chickens:  12
Number of bees:  0

Number of pigs:  6
Number of chickens:  13
Number of bees:  1

Number of pigs:  4
Number of chickens:  14
Number of bees:  2

Number of pigs:  2
Number of chickens:  15
Number of bees:  3

Number of pigs:  0
Number of chickens:  16
Number of bees:  4