path_sum.py

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def hasPathSum(self, root, sum):
        """
        :type root: TreeNode
        :type sum: int
        :rtype: bool
        """
        if root == None:
            return False
        if root.left == None and root.right == None: #leaf node
            return (sum == root.val)
        left = self.hasPathSum(root.left, sum-root.val)
        right = self.hasPathSum(root.right, sum-root.val)
        return (left or right)