题目
Find the sum of all left leaves in a given binary tree.
Example:
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3
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9 20
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15 7
There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.
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方法
递归遍历，如果为左节点，则打上标记isLeft，如果该节点没有左右子节点，则将该节点值累加到最后的结果中
python代码
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class (object):
def __init__(self, x):
self.val = x
self.left = None
self.right = None
class Solution(object):
def sumOfLeftLeaves(self, root):
self.result = 0
self.traverse(root)
return self.result
def traverse(self, node, isLeft=False):
if node and node.left == None and node.right == None and isLeft:
self.result += node.val
if node:
self.traverse(node.left, True)
self.traverse(node.right)
root = TreeNode(3)
root.left = TreeNode(9)
root.right = TreeNode(20)
root.right.left = TreeNode(15)
root.right.right = TreeNode(7)
assert Solution().sumOfLeftLeaves(root) == 24
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