import { TreeNode } from "../mod.ts";

export default function flatten(root: TreeNode | null): void {
    const list: TreeNode[] = [];
    preorderTraversal(root, list);
    const size = list.length;
    for (let i = 1; i < size; i++) {
        const prev = list[i - 1];
        const curr = list[i];
        prev.left = null;
        prev.right = curr;
    }
}
function preorderTraversal(root: TreeNode | null, list: TreeNode[]) {
    if (!root) return;
    list.push(root);
    preorderTraversal(root.left, list);
    preorderTraversal(root.right, list);
}