Find the sum of all left leaves in a given binary tree.
Example:
3
/ 9 20
/ 15 7
There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.
# 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 sumOfLeftLeaves(self, root):
"""
:type root: TreeNode
:rtype: int
"""
# Recursion method
‘‘‘
def rer(node,left):
if not node:
return 0
if left:
if node.left or node.right:
return rer(node.left,True)+rer(node.right,False)
else:
return node.val
else:
return rer(node.right,False)+rer(node.left,True)
return rer(root,False)
‘‘‘
# Non-recursion method
ans=0
if root:
stack=[root]
while stack:
node=stack.pop()
if node.left:
if not node.left.left and not node.left.right:
ans+=node.left.val
else:
stack.append(node.left)
if node.right:
stack.append(node.right)
return ans
[LeetCode&Python] Problem 404. Sum of Left Leaves
原文：https://www.cnblogs.com/chiyeung/p/10053015.html