Add solution for challenge #60

Author: Mauricio Klein

README.md

@@ -59,3 +59,4 @@
 - [x] [Challenge 57: Arithmetic Binary Tree](challenge-57/)
 - [x] [Challenge 58: Get all Values at a Certain Height in a Binary Tree](challenge-58/)
 - [x] [Challenge 59: Sort Colors](challenge-59/)
+- [x] [Challenge 60: Group anagrams](challenge-60/)

challenge-60/Makefile

@@ -0,0 +1,4 @@
+test:
+	python test_*.py
+
+.PHONY: test

challenge-60/README.md

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+# Group anagrams
+
+This problem was asked by RobinHood.
+
+## Description
+
+Given an array of strings, group anagrams together.
+
+## Example
+
+```
+Input: ['eat', 'ate', 'apt', 'pat', 'tea', 'now']
+Output: [
+          ['eat', 'ate', 'tea'],
+          ['apt', 'pat'],
+          ['now']
+        ]
+```

challenge-60/__init__.py

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+#
+# Time complexity : O(n*klogk) 
+#   (where n = number of anagrams, k = length of the largest anagram) 
+#   (klogk because we sort every anagram once)
+# Space complexity: O(n)
+#
+def group_anagrams(anagrams):
+  groups = {}
+
+  for word in anagrams:
+    sorted_word = ''.join(sorted(word))
+
+    if sorted_word in groups:
+      groups[sorted_word].append(word)
+    else:
+      groups[sorted_word] = [word]
+
+  return [g for g in groups.values()]

challenge-60/solver.py

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+import unittest
+from solver import group_anagrams
+
+class TestSolver(unittest.TestCase):
+  def test_group_anagrams(self):
+    anagrams = ['eat', 'ate', 'apt', 'pat', 'tea', 'now']
+    expected_groups = [['eat', 'ate', 'tea'],
+                       ['apt', 'pat'],
+                       ['now']]
+    self.assertItemsEqual(group_anagrams(anagrams), expected_groups)
+
+if __name__ == "__main__":
+    unittest.main()