二叉搜索树公共祖先

    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
    if(root.val > p.val && root.val > q.val) {
        return lowestCommonAncestor(root.left, p, q);
    } else if (root.val < p.val && root.val < q.val) {
        return lowestCommonAncestor(root.right, p, q);
    }
    return root;
}

二叉搜索树中的插入操作

    public TreeNode insertIntoBST(TreeNode root, int val) {
    if(root == null) {
        return new TreeNode(val);
    }
    if(root.val > val) {
        root.left = insertIntoBST(root.left, val);
    } else if(root.val < val) {
        root.right = insertIntoBST(root.right, val);
    }
    return root;
}

删除二叉搜索树中的节点

    public TreeNode deleteNode(TreeNode root, int key) {
    if(root == null) {
        return root;
    }
    if(root.val > key) {
        root.left = deleteNode(root.left, key);
    } else if(root.val < key) {
        root.right = deleteNode(root.right, key);
    } else {
        if(root.left == null) {
            return root.right;
        } else if(root.right == null) {
            return root.left;
        } else {
            TreeNode cur = root.right;
            while(cur.left != null) {
                cur = cur.left;
            }
            cur.left = root.left;
            return root.right;
        }
    }
    return root;
}