所有子字符串美丽值之和

/*
 * The beauty value of a string is defined as the difference between the
 * frequency of the most common character and the least common character.
 * For example, the beauty value of 'abaacc' is 3 - 1 = 2.
 * The task is to find the sum of the beauty values of all substrings of a given string.
 */

import java.util.stream.IntStream;
import java.util.stream.Stream;
import java.util.stream.Collectors;
import java.util.Arrays;

public class SolutionStream {
    public int beautySum(String s) {
        return IntStream.range(0, s.length())
                .flatMap(i -> IntStream.range(i + 1, s.length() + 1)
                        .map(j -> s.substring(i, j))
                        .mapToInt(substr -> {
                            int[] freq = new int[26];
                            substr.chars().forEach(ch -> freq[ch - 'a']++);
                            int maxFreq = Arrays.stream(freq).max().getAsInt();
                            int minFreq = Arrays.stream(freq)
                                    .filter(f -> f > 0)
                                    .min().getAsInt();
                            return maxFreq - minFreq;
                        }))
                .sum();
    }
}