112_PathSum.py

# coding: utf8


"""
    题目链接: https://leetcode.com/problems/path-sum/description.
    题目描述:

    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.

"""


# 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 not root:
            return False

        if not root.left and not root.right:
            return root.val == sum

        return self.hasPathSum(root.left, sum - root.val) or self.hasPathSum(root.right, sum - root.val)