在长度 2N 的数组中找出重复 N 次的元素

/*
 * Problem Statement:
 * Given an array nums with 2n elements, n+1 of them are unique, and one element repeats exactly n times.
 * The task is to find the element that repeats n times.
 *
 * Solution Approach:
 * 1. Use Java Stream API to create a frequency map of elements.
 * 2. Filter the map to find the element with frequency n and return it.
 */

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

public class FindRepeatingElementStream {
    public int repeatedNTimes(int[] nums) {
        int n = nums.length / 2;

        // Use Stream API to count frequencies of each element
        Map<Integer, Long> freqMap = Arrays.stream(nums)
                .boxed()
                .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

        // Find the element with frequency n
        return freqMap.entrySet().stream()
                .filter(entry -> entry.getValue() == n)
                .map(Map.Entry::getKey)
                .findFirst()
                .orElse(-1); // Return -1 if not found (shouldn't happen as per problem statement)
    }
}