```
/**
* 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) {
// base case
if(root==NULL)
return 0;
int sum = 0;
// if left is leaf, take left value
TreeNode *leftNode = root->left;
if(leftNode && leftNode->left == NULL && leftNode->right == NULL)
sum += leftNode->val;
// calculate for subtree and return sum
int left = sumOfLeftLeaves(root->left);
int right = sumOfLeftLeaves(root->right);
return sum+left+right;
}
};
```