Path Sum

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.

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

# 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 root == None:
            return False
        else:
            current = root
            s = []
            s.append(current)
            s.append(current.val)

            while s != []:
                pathsum = s.pop()
                current = s.pop()

                if not current.left and not current.right:
                    if pathsum == sum:
                        return True

                if current.right:
                    rightpathsum = pathsum + current.right.val
                    s.append(current.right)
                    s.append(rightpathsum)

                if current.left:
                    leftpathsum = pathsum + current.left.val
                    s.append(current.left)
                    s.append(leftpathsum)

            return False