Count Nice Pairs in an Array LeetCode solution in Java

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class Solution {
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  public int countNicePairs(int[] nums) {
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    final int mod = 1000000007;
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    int len = nums.length;
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    for (int i = 0; i < len; i++) {
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      nums[i] = nums[i] - reverse(nums[i]);
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    }
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    Arrays.sort(nums);
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    long res = 0;
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    for (int i = 0; i < len - 1; i++) {
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      long count = 1;
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      while (i < len - 1 && nums[i] == nums[i + 1]) {
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        count++;
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        i++;
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      }
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      res = (res % mod + (count * (count - 1)) / 2) % mod;
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    }
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    return (int) (res % mod);
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  }
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  private int reverse(int num) {
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    int rev = 0;
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    while (num > 0) {
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      rev = rev * 10 + num % 10;
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      num /= 10;
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    }
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    return rev;
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  }
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}