404. Sum of Left Leaves (Easy)
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.
题意:计算所有左叶子的和
思路:遍历二叉树
1.检查当前节点的左子节点是否是左子叶;
2.若是叶子节点,则返回左子叶的值加上对当前结点的右子节点调用递归的结果;
3.若不是叶子结点,我们对左右子节点分别调用递归函数,返回二者之和;
# Definition for a binary tree node. # class TreeNode(): # def __init__(self, x): # self.val = x # self.left = None # self.right = None class Solution(): def sumOfLeftLeaves(self, root): """ :type root: TreeNode :rtype: int """ ans = 0 l, r = root.left, root.right if root: if l and (l.left or l.right) is None: ans += l.val ans += self.sumOfLeftLeaves(l) + self.sumOfLeftLeaves(r) return ans