Update chapTree.tex

Eliminate useless variable.

node *pre is totally unused, why leave it there?

Author: frankvictor

C++/chapTree.tex

@@ -185,13 +185,12 @@ \subsubsection{Morris中序遍历}
 public:
     vector<int> inorderTraversal(TreeNode *root) {
         vector<int> result;
-        TreeNode *cur, *prev;
+        TreeNode *cur;
 
         cur = root;
         while (cur != nullptr) {
             if (cur->left == nullptr) {
                 result.push_back(cur->val);
-                prev = cur;
                 cur = cur->right;
             } else {
                 /* 查找前驱 */
@@ -201,12 +200,10 @@ \subsubsection{Morris中序遍历}
 
                 if (node->right == nullptr) { /* 还没线索化，则建立线索 */
                     node->right = cur;
-                    /* prev = cur; 不能有这句，cur还没有被访问 */
                     cur = cur->left;
                 } else {    /* 已经线索化，则访问节点，并删除线索  */
                     result.push_back(cur->val);
                     node->right = nullptr;
-                    prev = cur;
                     cur = cur->right;
                 }
             }