二叉查找树

public TreeNode insertNode(TreeNode root, TreeNode node) {
    if (root == null) {
        return node;
    }
    if (root.val >= node.val) {
        root.left = insertNode(root.left, node);
    }
    if (root.val < node.val) {
        root.right = insertNode(root.right, node);
    }
    return root;
}

public TreeNode insertNode(TreeNode root, TreeNode node) {
    if (root == null) {
        return node;
    }

    TreeNode cur = root;
    TreeNode last = null;

    while (cur != null) {
        last = cur;
        if (cur.val > node.val) {
            cur = cur.left;
        } else {
            cur = cur.right;
        }
    }

    if (last != null) {
        if (last.val > node.val) {
            last.left = node;
        } else {
            last.right = node;
        }
    }
    return root;
}