Find the sum of all left leaves in a given binary tree.

Example: 

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    3
   / \
  9  20
    /  \
   15   7
There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

思路

简单的递归求解即可。

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# 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
        """
        count = 0
        if (root == None):
            return 0
        if ((root.left) and (root.left.left == None) and (root.left.right == None)):
            count += root.left.val
        if ( (root.left) and ( (root.left.left) or (root.left.right) ) ):
            count += self.sumOfLeftLeaves(root.left)
        if ( (root.right) ):
            count += self.sumOfLeftLeaves(root.right)
        return count