[LeetCode] Flatten Binary Tree to Linked List

 1 class flat{
 2     public:
 3         void flatten(TreeNode* root) {
 4             if (root == NULL) return;
 5             stack<TreeNode*> s;
 6             s.push(root);
 7             while (!s.empty()) {
 8                 TreeNode *p = s.top();
 9                 s.pop();
10                 if (p->right)
11                     s.push(p->right);
12                 if (p->left)
13                     s.push(p->left);
14                 p->left = NULL;
15                 if (!s.empty())
16                     p->right = s.top();
17             }
18         }
19 };

 1 class flat{
 2     public:
 3             void  flatten_rec(TreeNode* root) {
 4             if (root == NULL) return;
 5             if(root->left == NULL && root->right == NULL)
 6                 return ;
 7 
 8             flatten_rec(root->left);
 9             flatten_rec(root->right);
10             
11             TreeNode * left_most = root->left;
12             while(left_most && left_most->right)
13             {
14                 left_most = left_most->right;
15             }
16             if(root->left != NULL)
17             {
18                 left_most->right = root->right;
19                 root->right = root->left;
20             }
21 
22             root->left = NULL;
23             return ;
24 
25         }
26 };