Create valid_parenthesis_permutations.py

Author: learning-zone

valid_parenthesis_permutations.py

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+# Given a num, get all the valid parenthesis permutations.
+# Observations:
+# - All permutations start with opens
+# - Base case: if num of open used == num of closed used
+# - Num of opens used up, then next to the end must be closed
+
+import unittest
+
+
+def valid_parens_perms(num):
+
+ result = []
+
+ def recurse(substr, left, right):
+ if left == 0 and right == 0:
+ result.append(substr)
+ return
+
+ elif left == 0:
+ recurse(substr + ')', left, right - 1)
+
+ elif left < right:
+ recurse(substr + '(', left - 1, right)
+ recurse(substr + ')', left, right - 1)
+
+ elif left == right:
+ recurse(substr + '(', left - 1, right)
+
+ recurse('', num, num)
+
+ return result
+
+
+class Testing(unittest.TestCase):
+ def test_valid_parens_perms(self):
+ self.assertEqual(valid_parens_perms(1), ['()'])
+ self.assertEqual(valid_parens_perms(2), ['(())', '()()'])
+ self.assertEqual(valid_parens_perms(3), ['((()))', '(()())', '(())()', '()(())', '()()()'])
+ self.assertEqual(valid_parens_perms(4), ['(((())))', '((()()))', '((())())', '((()))()', '(()(()))', '(()()())', '(()())()', '(())(())', '(())()()', '()((()))', '()(()())', '()(())()', '()()(())', '()()()()'])
+
+
+if __name__ == '__main__':
+ unittest.main()