class Node {

    constructor(val) {

        this.val = val;

        this.left = null;

        this.right = null;

    }

}

​

function leastCommonAncestor(root, node1, node2) {

    if (root.val > node1 && root.val > node2) {

        return leastCommonAncestor(root.left, node1, node2);

    } else if (root.val < node1 && root.val < node2) {

        return leastCommonAncestor(root.right, node1, node2);

    } else {

        return root;

    }

}

​

//       7

//      / \

//     4   8

//    / \

//   1  5

​

const root = new Node(7);

root.left = new Node(4);

root.left.left = new Node(1);

root.left.right = new Node(5);

root.right = new Node(8);