LeetCode404. Sum of Left Leaves（思路及python解法）

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.

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这道题比较简单，不过感觉说的不是很清楚，只是求所有左叶子节点的和。

用bfs算法，层序遍历。

如果这个节点是左子树，而且是叶子节点，则把和相加。

class Solution:
    def sumOfLeftLeaves(self, root: TreeNode) -> int:
        if root is None:return 0
        bfs=[root]
        res=0
        while bfs:
            temp=[]
            for node in bfs:
                if node.left:
                    temp.append(node.left)
                    if (node.left.left or node.left.right) is None:
                        res+=node.left.val
                if node.right:temp.append(node.right)
            bfs=temp
        return res