Increasing Order Search Tree LeetCode solution in Java

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class Solution {
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  TreeNode inRoot = new TreeNode();
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  TreeNode temp = inRoot;
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  public TreeNode increasingBST(TreeNode root) {
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    inorder(root);
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    return inRoot.right;
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  }
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  public void inorder(TreeNode root) {
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    if (root == null) return;
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    inorder(root.left);
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    temp.right = new TreeNode(root.val);
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    temp = temp.right;
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    inorder(root.right);
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  }
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}