[Leetcode] Binary tree--112. Path Sum

112. 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.

 

Solution:

1. use iterative way;  bfs 

 1   if root is None: 2             return False 3         d = deque() 4          5         d.append((root, root.val)) 6  7         while(len(d)): 8             nodeInfo = d.popleft() 9             node = nodeInfo[0]10             s = nodeInfo[1]11             if (not node.left) and (not node.right):12                 if s == sum:13                     return True14             if node.left:15                 d.append((node.left, s + node.left.val))16             if node.right:17                 d.append((node.right, s + node.right.val))18         return False

 

 2. use recursive way

 1         return self.haspathSumHelper(root, 0, sum) 2          3     def haspathSumHelper(self, node, current, sum): 4          5         if node is None: 6             return False 7         current += node.val 8         if (not node.left ) and (not node.right): 9             if current == sum:10                 return True11             else:12                 return False13             14         15         return self.haspathSumHelper(node.left, current, sum) or self.haspathSumHelper(node.right, current, sum)