897. Increasing Order Search Tree

#### QUESTION:

Given a tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has no left child and only 1 right child.

Example 1:
Input: [5,3,6,2,4,null,8,1,null,null,null,7,9]

5
/ \
3    6
/ \    \
2   4    8
/        / \
1        7   9

Output: [1,null,2,null,3,null,4,null,5,null,6,null,7,null,8,null,9]

1
\
2
\
3
\
4
\
5
\
6
\
7
\
8
\
9

Note:

1. The number of nodes in the given tree will be between 1 and 100.
2. Each node will have a unique integer value from 0 to 1000.

#### SOLUTION:

class Solution {
public TreeNode increasingBST(TreeNode root) {
TreeNode head = increasingBSTResult;
increasingBSTHelper(root);
return head.right;
}
public TreeNode increasingBSTResult = new TreeNode(0);
public void increasingBSTHelper(TreeNode node){
if(node==null) return;
increasingBSTHelper(node.left);
TreeNode right = new TreeNode(node.val);
increasingBSTResult.right = right;
increasingBSTResult = right;
increasingBSTHelper(node.right);
}
}
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