统计平方和三元组的数目

/*
 * Solution using Java Streams to find the number of Pythagorean triplets (a, b, c)
 * where a^2 + b^2 = c^2 and 1 <= a, b, c <= n.
 */
import java.util.stream.IntStream;

public class PythagoreanTripletsStream {
    public long countTriplets(int n) {
        return IntStream.rangeClosed(1, n) // Iterate over a
            .boxed()
            .flatMap(a -> IntStream.rangeClosed(a, n) // Iterate over b, starting from a
                .mapToObj(b -> new int[]{a, b, (int) Math.sqrt(a * b)}) // Calculate c
                .filter(triplet -> triplet[2] <= n && triplet[2] * triplet[2] == triplet[0] * triplet[0] + triplet[1] * triplet[1]) // Check if triplet is valid
            ).count(); // Count valid triplets
    }

    public static void main(String[] args) {
        PythagoreanTripletsStream pts = new PythagoreanTripletsStream();
        System.out.println(pts.countTriplets(5)); // Output: 2
        System.out.println(pts.countTriplets(10)); // Output: 4
    }
}