LeetCode#112 Path Sum

Problem Definition:

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.

For 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.

Solution: 从根节点开始，减去当前值，往下。

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

class Solution:
# @param {TreeNode} root
# @param {integer} sum
# @return {boolean}
def hasPathSum(self, root, sum):
if root==None:
return False
if root.val==sum and root.left==None and root.right==None:
return True
return self.hasPathSum(root.left,sum-root.val)\
or self.hasPathSum(root.right,sum-root.val)