Leetcode 112: Path Sum

https://leetcode.com/problems/path-sum-ii/

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.

 

Code

# 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: intyy
        :rtype: List[List[int]]
        """
        if root is None: return False
        if root.left is None and root.right is None: return sum==root.val
        
        left = self.hasPathSum(root.left, sum-root.val) if root.left else False
        right = self.hasPathSum(root.right, sum-root.val) if root.right else False
        return left or right

 

Idea

Use DFS to traverse nodes.