LeetCode 404. Sum of Left Leaves

3
/ \
9  20
/  \
15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int sumOfLeftLeaves(TreeNode* root) {
if(!root) return 0;
int left = 0, right = 0;
if(root->left){
if(!root->left->left && !root->left->right) left = root->left->val;
else left = sumOfLeftLeaves(root->left);
}
if(root->right){
if(!root->right->left && !root->right->right) right = 0;
else right = sumOfLeftLeaves(root->right);
}
return left + right;
}
};