Find the Closest Palindrome LeetCode solution in Java

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class Solution {
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  static long pow(long base, long exp) {
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    long ans = 1;
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    for (; exp != 0; ) {
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      if ((exp & 1) == 1) {
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        ans *= base;
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      }
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      base *= base;
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      exp >>= 1;
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    }
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    return ans;
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  }
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  public String nearestPalindromic(String n) {
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    long num = Long.parseLong(n);
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    if (num <= 10) {
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      return String.valueOf(num - 1);
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    }
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    long comp[] = new long[5];
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    comp[0] = pow(10, n.length() - 1) - 1;
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    comp[1] = pow(10, n.length()) + 1;
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    int mid = (n.length() + 1) / 2;
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    long half = Long.parseLong(n.substring(0, mid));
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    long pref[] = {half, half + 1, half - 1};
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    for (int i = 0; i < 3; i++) {
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      StringBuilder st = new StringBuilder(String.valueOf(pref[i]));
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      if (n.length() % 2 == 1) st.deleteCharAt(st.length() - 1);
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      st.reverse();
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      comp[i + 2] = Long.parseLong(String.valueOf(pref[i]) + st.toString());
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    }
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    long min = Long.MAX_VALUE;
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    long ans = Long.MAX_VALUE;
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    for (int i = 0; i < 5; i++) {
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      long dif = Math.abs(num - comp[i]);
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      if (dif != 0 && min > dif) {
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        min = dif;
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        ans = comp[i];
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      } else if (min == dif) ans = Math.min(ans, comp[i]);
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    }
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    return String.valueOf(ans);
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  }
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}