Number of Different Subsequences GCDs LeetCode solution in Java

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class Solution {
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  int max = 0;
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  Set<Integer> exist = new HashSet();
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  public int countDifferentSubsequenceGCDs(int[] nums) {
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    getMax(nums);
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    for (int num : nums) exist.add(num);
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    int count = 0;
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    for (int i = 1; i <= max; i++) if (findGCD(i)) count++; //  <---- findGCD
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    return count;
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  }
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  public void getMax(int[] nums) {
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    for (int i : nums) max = Math.max(max, i);
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  }
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  public int gcd(int a, int b) {
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    return (a == 0) ? b : gcd(b % a, a);
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  }
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  public boolean findGCD(int num) {
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    int val = 0;
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    for (int i = num; i <= max; i += num)
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      if (exist.contains(i)) val = gcd(i, val); //  <---- gcd between two number
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    return (val == num);
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  }
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}