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Recursion for Coding Interviews in Python

Solution Review: Balance Parenthesis

Understand how to apply recursion to verify if an array of parentheses is balanced by tracking opening and closing brackets with indices. Learn base and recursive cases to solve this common coding interview problem.

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Solution: Using Recursion

Python 3.5
def balanced(testVariable, startIndex = 0, currentIndex = 0) :
  # Base case1 and 2
  if startIndex == len(testVariable) : 
    return currentIndex == 0
  # Base case3
  if currentIndex < 0 : # A closing bracket did not find its corresponding opening bracket
    return False
  # Recursive case1
  if testVariable[startIndex] == "(" : 
    return  balanced(testVariable, startIndex + 1, currentIndex + 1)
  # Recursive case2
  elif testVariable[startIndex] == ")" : 
    return  balanced(testVariable, startIndex + 1, currentIndex - 1)
# Driver Code
testVariable = ["(", "(", ")", ")", "(", ")"]
print(balanced(testVariable))

Explanation

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