Numbers With Same Consecutive Differences LeetCode solution in Java

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class Solution {
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  List<Integer> res = new ArrayList<>();
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  public int[] numsSameConsecDiff(int n, int k) {
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    for (int ans = 1; ans < 10; ans++) { // first digit can't be 0
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      find(ans, n - 1, k); // find remaining n-1 digits using backtrack
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    }
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    return res.stream().mapToInt(Integer::intValue).toArray(); // convert list to int arr
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  }
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  private void find(int ans, int n, int k) {
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    if (n == 0) {
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      res.add(ans); // if got length n number then put that into res
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      return;
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    }
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    for (int i = 0; i < 10; i++) {
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      if (Math.abs(ans % 10 - i) == k) // find digit that have k difference with last digit
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      find(ans * 10 + i, n - 1, k);
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    }
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    ans /= 10; // remove last digit while backtrack
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  }
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}