Construct Binary Tree from Inorder and Postorder Traversal LeetCode solution in Java

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class Solution {
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  int[] io;
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  int[] po;
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  int n; // nth post order node
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  public TreeNode buildTree(int[] inorder, int[] postorder) {
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    this.n = inorder.length - 1;
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    this.io = inorder;
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    this.po = postorder;
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    return buildTree(0, n);
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  }
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  public TreeNode buildTree(int low, int high) {
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    if (n < 0 || low > high) return null;
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    int currNode = po[n--];
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    int idxInInorder = low;
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    TreeNode root = new TreeNode(currNode);
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    if (low == high) return root; // no more nodes
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    while (io[idxInInorder] != currNode) idxInInorder++; // find index of currNode in inorder
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    root.right = buildTree(idxInInorder + 1, high);
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    root.left = buildTree(low, idxInInorder - 1);
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    return root;
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  }
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}