Add solution for challenge #34

Author: Mauricio Klein

README.md

@@ -33,3 +33,4 @@
 - [x] [Challenge 31: Find cycle in indirected graph](challenge-31/)
 - [x] [Challenge 32: Shortest path in a indirected acyclic graph](challenge-32/)
 - [x] [Challenge 33: Merge Overlapping Intervals](challenge-33/)
+- [x] [Challenge 34: Subset sum problem](challenge-34/)

challenge-34/Makefile

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

challenge-34/README.md

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+# Subset sum problem
+
+## Description
+
+Given a set of non-negative integers, and a value sum, determine if there is a subset of the given set with sum equal to given sum.
+
+## Example
+
+```
+Input: 
+set = (3, 34, 4, 12, 5, 2), sum = 9
+
+Output: 
+True # subset (4, 5) are equal to 9
+```

challenge-34/__init__.py

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+def subset_sum(nums, target):
+  return helper(0, nums, target)
+
+def helper(acc, remaining_nums, target):
+  if acc == target:
+    return True
+  elif acc > target:
+    return False
+  elif not remaining_nums:
+    return False
+
+  num = remaining_nums[0]
+
+  # Return the backtracking with and without the next number
+  return helper(acc+num, remaining_nums[1:], target) or helper(acc, remaining_nums[1:], target)

challenge-34/solver.py

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+import unittest
+from solver import subset_sum
+
+class TestSolver(unittest.TestCase):
+  def test_queen(self):
+    self.assertTrue (subset_sum((3, 34, 4, 12, 5, 2), 8)) # True: (3,5)
+    self.assertFalse(subset_sum((3, 34, 4, 12, 5, 2), 1)) # False
+    self.assertTrue (subset_sum((1,  1, 1,  1, 1   ), 5)) # True: (1,1,1,1,1)
+    self.assertFalse(subset_sum((1,  1, 1,  1, 1   ), 6)) # False
+    self.assertTrue (subset_sum((                  ), 0)) # True: ()
+
+if __name__ == "__main__":
+    unittest.main()