题目描述：
https://leetcode-cn.com/problems/sum-of-left-leaves/
代码：
递归
class Solution {
public:
int sumOfLeftLeaves(TreeNode* root) {
return SumOfLeft(root, false);
}
int SumOfLeft(TreeNode* root, bool flag)
{
if(!root)
return 0;
if(!root->left && !root->right && flag)
return root->val;
return SumOfLeft(root->left, true) + SumOfLeft(root->right, false);
}
};
