好数对的数目

/*
 * Approach:
 * We can use Java Streams to solve this problem in a more functional way.
 * We'll use a combination of IntStream and flatMap to generate all pairs of indices (i, j) where i < j.
 * Then, we'll filter these pairs to find the good pairs where nums[i] == nums[j].
 * Finally, we'll count the number of such pairs.
 */
import java.util.stream.IntStream;

public class GoodPairsStream {
    public static int numIdenticalPairs(int[] nums) {
        return (int) IntStream.range(0, nums.length)
                .flatMap(i -> IntStream.range(i + 1, nums.length)
                        .filter(j -> nums[i] == nums[j]))
                .count();
    }

    public static void main(String[] args) {
        int[] nums = {1, 2, 3, 1, 1, 3};
        System.out.println(numIdenticalPairs(nums)); // Output: 4
    }
}