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

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class Solution {
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  Map<Integer, Integer> inMap;
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  int curIndex = 0;
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  int[] preOrder;
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  public TreeNode buildTree(int[] preorder, int[] inorder) {
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    preOrder = preorder;
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    inMap = new HashMap<>();
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    for (int i = 0; i < inorder.length; i++) {
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      inMap.put(inorder[i], i);
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    }
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    return dfs(0, preorder.length - 1);
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  }
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  public TreeNode dfs(int s, int e) {
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    if (s > e) return null;
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    int curNode = preOrder[curIndex++];
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    TreeNode root = new TreeNode(curNode);
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    int inRoot = inMap.get(curNode);
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    root.left = dfs(s, inRoot - 1);
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    root.right = dfs(inRoot + 1, e);
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    return root;
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  }
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}