Sum of Left Leaves

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.

int sumOfLeftLeaves(struct TreeNode* root) {
    if(!root) return 0;
    if(root->left&&!root->left->left&&!root->left->right) return root->left->val + sumOfLeftLeaves(root->right);
    return sumOfLeftLeaves(root->left) + sumOfLeftLeaves(root->right);
}