森林中的兔子

// Problem Statement: In a forest, we have an unknown number of rabbits. Some rabbits are asked, "How many rabbits have the same color as you?" and their answers are collected in an integer array 'answers'. The task is to find the minimum number of rabbits that could be in the forest based on their answers.

// Solution approach:
// 1. Stream the answers to count occurrences of each number.
// 2. Calculate the minimum number of rabbits for each group based on their answers.
// 3. Sum up the results for all groups to get the total minimum number of rabbits.

import java.util.Arrays;
import java.util.Map;
import java.util.stream.Collectors;

public class RabbitsInForestStream {
    public int numRabbits(int[] answers) {
        return Arrays.stream(answers)
                .boxed()
                .collect(Collectors.groupingBy(a -> a, Collectors.counting()))
                .entrySet()
                .stream()
                .mapToInt(entry -> {
                    int groupSize = entry.getKey() + 1;
                    int groupCount = Math.toIntExact(entry.getValue());
                    int numberOfGroups = (int) Math.ceil((double) groupCount / groupSize);
                    return numberOfGroups * groupSize;
                })
                .sum();
    }
}