[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 True
14             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 True
11             else:
12                 return False
13
14
15         return self.haspathSumHelper(node.left, current, sum) or self.haspathSumHelper(node.right, current, sum)