```
class Solution {
int sum=0;
public:
int sumOfLeftLeaves(TreeNode* root) {
if(!root) return 0;
if(root->left!=NULL&&root->left->left==NULL&&root->left->right==NULL)
return root->left->val+sumOfLeftLeaves(root->right);
else return sumOfLeftLeaves(root->left)+sumOfLeftLeaves(root->right);
}
};
```