404. Sum of Left Leaves

Easy

661

75

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Share 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.

思路：深度搜索算法，是左子树，且没有子节点，add

代码：python3

class Solution(object):
    def sumOfLeftLeaves(self, root):
        cache=[0]
        def dfs(root,left):
            if not root:return
            if left and not root.left and not root.right:
                cache[0] += root.val
            dfs(root.left,True)
            dfs(root.right,False)
        dfs(root,False)
        return cache[0]