1     void flatten(TreeNode* root) {
 2         TreeNode* curNode = root;
 3         while (curNode) {
 4             if (curNode -> left) {
 5                 TreeNode* predecessor = curNode -> left;
 6                 while (predecessor -> right)
 7                     predecessor = predecessor -> right;
 8                 predecessor -> right = curNode -> right;
 9                 curNode -> right = curNode -> left;
10                 curNode -> left = NULL;
11             }
12             else curNode = curNode -> right;
13         }
14     }