Decompress Run-Length Encoded List LeetCode solution in Java

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class Solution {
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  public int[] decompressRLElist(int[] nums) {
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    ArrayList<Integer> arr = new ArrayList<>();
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    for (int i = 0; i + 1 < nums.length; i += 2) {
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      for (int j = 0; j < nums[i]; ++j) {
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        arr.add(nums[i + 1]);
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      }
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    }
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    int[] res = new int[arr.size()];
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    for (int i = 0; i < res.length; ++i) res[i] = arr.get(i);
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    return res;
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  }
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}