[Feature] Added combinations of phone numbers. Minified permutation code.

Author: exterkamp

README.md

@@ -60,4 +60,6 @@ Different algorithmic programs.  Grouped by general topic.
 #### String Based Algorithms
 * [Fizz Buzz](algorithms/string/fizz_buzz.py)
 * [Permutations](algorithms/string/permutations.py)
-* [Combinations](algorithms/string/combinations.py)
+* [Combinations](algorithms/string/combinations.py)
+  * [Letters in Word](algorithms/string/combinations.py)
+  * [Letters from Phone](algorithms/string/combinations.py)

algorithms/string/combinations.py

@@ -10,3 +10,39 @@ def combinations_of_word(string: str):
             output.append(string[i:j+1])
 
     return output
+
+def combinations_of_phone_input(string: str):
+    """
+    Find all permutations of phone numbers in an input of numbers.
+
+    While not a 'combination' of numbers in the mathematical sense
+    this is known more lexically as a combination.  But does not 
+    contain all combinations possible.  Only combinations that are
+    full length using all input numbers in the string.
+
+    """
+    phone_mapper = {
+            '1' : [],
+            '2' : ['a','b','c'],
+            '3' : ['d','e','f'],
+            '4' : ['g','h','i'],
+            '5' : ['j','k','l'],
+            '6' : ['m','n','o'],
+            '7' : ['p','q','r','s'],
+            '8' : ['t','u','v'],
+            '9' : ['w','x','y','z'],
+        }
+    
+    outputs = [letter for letter in phone_mapper[string[0]]]
+        
+    for i in range(1,len(string)):
+        temp = []
+        for output in outputs:
+            temp = temp + [output + letter for letter in phone_mapper[string[i]]]
+        outputs = temp
+    
+    return outputs    
+
+
+
+

algorithms/string/permutations.py

@@ -8,8 +8,7 @@ def permute(current, remaining):
             permute.list.append(current)
             return
         for i in range(0,len(remaining)):
-            remaining_minus = remaining[0:i] + remaining[i+1:]
-            permute(current + remaining[i], remaining_minus)
+            permute(current + remaining[i], remaining[:i] + remaining[i+1:])
 
     permute.list = []
     permute('', list(string))

tests/test_combinations_phone.py

@@ -0,0 +1,7 @@
+import unittest
+from algorithms.string.combinations import combinations_of_phone_input
+
+class TestCombinationsPhone(unittest.TestCase):
+
+    def test_phone_combo_simple(self):
+        self.assertEqual(['da', 'db', 'dc', 'ea', 'eb', 'ec', 'fa', 'fb', 'fc'], combinations_of_phone_input('32'))