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)