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import { TreeNode } from "../binary-tree-inorder-traversal/TreeNode.ts";
export default sumOfLeftLeaves;
function sumOfLeftLeaves(root: TreeNode | null): number {    if (!root) return 0;    const sum = root.left && !root.left.left && !root.left.right        ? root.left.val        : 0;    return sum + sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right);}