public class Solution { TreeNode pre=null; public TreeNode Convert(TreeNode pRootOfTree) { if(pRootOfTree==null) return null; Convert(pRootOfTree.right); if(pre==null) pre=pRootOfTree; else{ pRootOfTree.right=pre; pre.left=pRootOfTree; pre=pRootOfTree; } Convert(pRootOfTree.left); return pre; }}