Leon Lin’s Blog Path-Sum

##Path Sum
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.

class Solution:

# @param sum, an integer
# @return a boolean
def (self, root, sum):
    if root is None:
        return False
    if root.right is None and root.left is None:
        return root.val == sum
    return self.hasPathSum(root.left, sum - root.val) or self.hasPathSum(root.right, sum - root.val)