112. Path Sum

Posted 2020-09-05

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.

 

 1 # Definition for a binary tree node.
 2 # class TreeNode(object):
 3 #     def __init__(self, x):
 4 #         self.val = x
 5 #         self.left = None
 6 #         self.right = None
 7 
 8 class Solution(object):
 9     def hasPathSum(self, root, sum):
10         """
11         :type root: TreeNode
12         :type sum: int
13         :rtype: bool
14         """
15         if not root:
16             return False
17 
18         if not root.left and not root.right and root.val == sum:
19             return True
20         
21         sum -= root.val
22 
23         return self.hasPathSum(root.left, sum) or self.hasPathSum(root.right, sum)