112. Path Sum

Problem

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

      5
     / \
    4   8
   /   / \
  11  13  4
 /  \      \
7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

Thought Process & White Board

Code

class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution:
    def hasPathSum(self, root, num):

        if root is None:
            return False

        if root.left is None and root.right is None:
            return root.val == num

        if self.hasPathSum(root.left, num - root.val):
            return True

        if self.hasPathSum(root.right, num - root.val):
            return True