first commit

thumbtack_challenge_1.py

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+from __future__ import division
+import sys
+from collections import defaultdict
+
+""" write a program that takes in four numbers and determines the \
+mathematical expression that can combine the first three numbers, \
+through addition, subtraction, multiplication, and division, to  \
+get the fourth.
+
+e.g. echo '1 2 3 5' | python challenge.py
+$ 3 + 2 * 1
+
+e.g. echo '1 1 1 6' | python challenge.py
+$ 4 / 6 * 3
+
+"""
+
+operators = ["*", "/", "+", "-"]
+
+
+def split_input(arg):
+    """splits input by spaces"""
+    the_nums = arg.readline().rstrip().split(" ")
+    return the_nums
+
+
+def validate_input(arg):
+    """tests whether the arg is an integer; quits if not"""
+    if "." in arg or any([l.isalpha() for l in arg]):
+        print "only integers, please."
+        return sys.exit()
+    else:
+        arg = int(arg)
+    return arg
+
+
+def split_into_three_and_one(a_list_of_numbers):
+    first_three = []
+    for i in range(3):
+        first_three.append(a_list_of_numbers[i])
+    should_equal = int(a_list_of_numbers[3])
+    return first_three, should_equal
+
+
+def do_math_on_two_numbers(first_number, second_number, operator):
+    first_number = int(first_number)
+    second_number = int(second_number)
+    if operator == "+":
+        return sum([first_number, second_number])
+    if operator == "-":
+        return first_number - second_number
+    if operator == "*":
+        return first_number * second_number
+    if operator == "/":
+        return first_number / second_number
+
+
+def do_each_possible_math_operation(first_number, second_number):
+    the_total = defaultdict(str)
+    for operator in operators:
+        the_total[operator] = do_math_on_two_numbers(first_number,
+                                                     second_number, operator)
+    return the_total
+
+
+def test_if_first_three_equals_four(list_of_nums, should_equal):
+    for i in range(len(list_of_nums)):
+        totals = do_each_possible_math_operation(list_of_nums[i],
+                                                 list_of_nums[i-1])
+        for first_operator, first_total in totals.iteritems():
+            for second_operator, second_total in \
+                do_each_possible_math_operation(first_total,
+                                                list_of_nums[i-2]).iteritems():
+                if second_total == should_equal:
+                    return list_of_nums[i], first_operator, list_of_nums[i-1], \
+                        second_operator, list_of_nums[i-2]
+
+if __name__ == "__main__":
+    the_nums = split_input(sys.stdin)
+    for num in the_nums:
+        validate_input(num)
+    first_three, should_equal = split_into_three_and_one(the_nums)
+    initial_results = test_if_first_three_equals_four(first_three,
+                                                      should_equal)
+    try:
+        first, first_op, second, second_op, third = initial_results
+    except:
+        print "Invalid."
+        sys.exit()
+    print first, first_op, second, second_op, third