Sorry if this is a general question but I am a beginner in Python and many times when I see other people code using recursion, they create a helper function for the main function and then call that helper function which itself is recursive.
This seems a bit different from the simplest cases of recursion for example (sum of lists, factorial) where the function only calls itself.
Can someone explain this technique more carefully perhaps with examples?
Much appreciated.
Example 1: (Reversing linked list using recursion)
def revert_list(self):
self.head = self._revert_helper(self.head)
def _revert_helper(self, node):
temp = None
if node.forward == None:
return node
else:
temp = self._revert_helper(node.forward)
node.forward.forward = node
node.forward = None
return temp
Example 2: (Binary Search Tree)
def __contains__(self, key):
return self._bstSearch(self._root, key)
# Returns the value associated with the key.
def valueOf(self, key):
node = self._bstSearch(self._root, key)
assert node is not None, "Invalid may key."
return node.value
# Helper method that recursively searches the tree for a target key:
# returns a reference to the Node. This allows
# us to use the same helper method to implement
# both the contains and valueOf() methods of the Map class.
def _bstSearch(self, subtree, target):
if subtree is None: # base case
return None
elif target < subtree.key: # target is left of the subtree root
return self._bstSearch(subtree.left)
elif target > subtree.key: # target is right of the subtree root
return self.bstSearch(subtree.right)
else: # base case
return subtree