public void deleteEdge(TreeNode root) {

     if(root == null) return;

     root = dfs(root, Integer.MIN_VALUE, Integer.MAX_VALUE);

 }

 private TreeNode dfs(TreeNode root, int left, int right) {

     if(root == null) return null;

     if(root.val <= left || root.val >= right) return null;

     root.left = dfs(root.left, left, root.val);

     root.right = dfs(root.right, root.val, right);

     return root;

 }