leetcode[156]Binary Tree Upside Down

Given a binary tree where all the right nodes are either leaf nodes with a sibling (a left node that shares the same parent node) or empty, flip it upside down and turn it into a tree where the original right nodes turned into left leaf nodes. Return the new root.

For example:
Given a binary tree {1,2,3,4,5},
1
/ \
2 3
/ \
4 5

return the root of the binary tree [4,5,2,#,#,3,1].
4
/ \
5 2
  / \
 3 1

   TreeNode *upsideDownBinaryTree(TreeNode *root)

   {

       if(root == NULL)

           return root;

 

       stack<TreeNode*> s;    //left child list

       s.push(root);

       TreeNode* cur = root;

       while(cur->left)

       {

           s.push(cur->left);

           cur = cur->left;

       }

       TreeNode* newroot = s.top();

       cur = newroot;

       s.pop();

       while(!s.empty())

       {

           TreeNode* oldfather = s.top();

           s.pop();

           cur->left = oldfather->right;

           cur->right = oldfather;

           oldfather->left=NULL;

           oldfather->right=NULL;

           cur = curr->left;

       }

       return newroot;

   }