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Hash Tables: Ice Cream Parlor

  • DagnyT + 1 comment

    @Dan_Golding

    I just ran a small test to check if the Map[cost] to FlavorIdx approach has a bug in it. It does. This is why Gayle's YouTube video uses BinarySearch on Cost entries ordered by FlavorIdx.

    In this test sequence; the Flavor at position 2 overwrites/loses the flavor at position 1.

    What's interesting though; is that this test case appears to be missing from the Hacker Rank test suite; because this Map[cost] code approach was passing all of their test suite.

    Here's my Python code (formatted on next comment):

    • DagnyT + 1 comment
      def find_matched_flavors(m, a):
    print "TOTAL MONEY is:  {0}".format(m)
    cost_map = {}
    for i, cost in enumerate(a):
        print "(i, cost) is ({0},{1})".format(i, cost)
        sunny = cost
        johnny = m - cost
        print "prior cost_map {0}".format(cost_map)
        print "johnny, sunny {0}, {1}".format(johnny, sunny)
        if johnny in cost_map.keys():
            print "FOUND MATCHED FLAVORS IN ORDER OFFSET +1:"
            print cost_map[johnny]+1, i+1
        # BUGFIXED:  following else blocks add of NEW cost:flavorIdx if complement already found pre-loaded
        # else:
        # BUG-UNFIXED:  following with OVERWRITE-LOSE prior flavor with cost duplicating CURRENT flavor cost!
        #               eg. (5, 0) gets overwritten with (5, 1)
        #               i.e. complement must be found on FIRST cost map entry; otherwise we lose all history of
        #               that entry when a duplicate cost entry is added!
        cost_map[cost] = i
        print "updated cost_map {0}".format(cost_map)
  
# MY TEST SCRIPT 

m = 8
flavorsToCost = [5, 5, 3, 4, 4]
find_matched_flavors(m, flavorsToCost)
      • Dan_Golding + 1 comment

        The problem specifies that there will only be one unique solution. Your test case has three valid solutions (i.e. (0,2), (1,2) and (3,4)) and so it is not a valid test case for the problem defined.

        • MisterTB + 0 comments

          i agree, undefined in case there are 3 (or more) similar costs.