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class Solution {
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  public long appealSum(String s) {
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    long res = 0;
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    char[] cs = s.toCharArray();
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    int n = cs.length;
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    int[] pos = new int[26];
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    Arrays.fill(pos, -1);
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    for (int i = 0; i < n; ++i) {
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      int j = cs[i] - 'a', prev = pos[j];
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      res += (i - prev) * (long) (n - i);
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      pos[j] = i;
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    }
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    return res;
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  }
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}