class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        int res=0;
        if(root == null) return 0;
        if(root.left != null){
            if(root.left.left == null && root.left.right == null) res += root.left.val;
            else res += sumOfLeftLeaves(root.left);
        }
        
        res+=sumOfLeftLeaves(root.right);
        
        return res;
    }
}