Maximum Sum Obtained of Any Permutation LeetCode solution in Java

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class Solution {
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  public int maxSumRangeQuery(int[] nums, int[][] requests) {
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    int n = nums.length;
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    int[] pref = new int[n];
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    for (int i = 0; i < requests.length; i++) {
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      pref[requests[i][0]]++;
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      if (requests[i][1] + 1 < n) pref[requests[i][1] + 1]--;
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    }
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    for (int i = 1; i < n; i++) {
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      pref[i] += pref[i - 1];
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    }
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    Arrays.sort(nums);
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    Arrays.sort(pref);
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    long res = 0;
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    for (int i = 0; i < n; i++) {
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      res += ((long) pref[i] * nums[i]);
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      res %= 1000000007;
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    }
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    return (int) res % 1000000007;
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  }
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}