Longest Ideal Subsequence LeetCode solution in Java

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class Solution {
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  public int longestIdealString(String s, int k) {
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    int DP[] = new int[26], ans = 1;
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    for (int ch = 0, n = s.length(); ch < n; ch++) {
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      int i = s.charAt(ch) - 'a';
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      DP[i] = DP[i] + 1;
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      for (int j = Math.max(0, i - k); j <= Math.min(25, i + k); j++)
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        if (j != i) DP[i] = Math.max(DP[i], DP[j] + 1);
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      ans = Math.max(ans, DP[i]);
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    }
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    return ans;
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  }
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}