Problem:
Score : 300 points

Problem Statement

You are given integers N and K. Find the number of triples (a,b,c) of positive integers not greater than N such that a+b,b+c and c+a are all multiples of K.
The order of a,b,c does matter, and some of them can be the same.

Constraints

1 \leq N,K \leq 2\times 10^5

N and K are integers.

Input

Input is given from Standard Input in the following format:

N K

Output

Print the number of triples (a,b,c) of positive integers not greater than N such that a+b,b+c and c+a are all multiples of K.

Sample Input 1

3 2

Sample Output 1

9

(1,1,1),(1,1,3),(1,3,1),(1,3,3),(2,2,2),(3,1,1),(3,1,3),(3,3,1) and (3,3,3) satisfy the condition.

Sample Input 2

5 3

Sample Output 2

1

Sample Input 3

31415 9265

Sample Output 3

27

Sample Input 4

35897 932

Sample Output 4

114191

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Time Limit Exceeded)

import java.util.*;

public class Main {
    public static void main(String... a) {
        Scanner s = new Scanner(System.in);
        String input = s.nextLine();
        String[] xys = input.split(" ");

        int N = Integer.parseInt(xys[0]);
        int K = Integer.parseInt(xys[1]);

        long cnt = 0;

        // System.out.println(N);
        // System.out.println(K);

        for (int i = 1; i <= N; i++) {
            List<Integer> jList = new ArrayList<>();
            for (int ii = 0; ; ++ii) {
                int j = K - i + ii * K;
                if (j <= 0) continue;
                if (j > N) break;

                jList.add(j);
            }

            for (int j : jList) {
                if ((i + j) % K != 0) {
                    continue;
                }

            Set<Integer> kList = new HashSet<>();
            for (int ii = 0; ; ++ii) {
                int k = K - j + ii * K;
                if (k <= 0) continue;
                if (k > N) break;
                kList.add(k);
            }

            for (int ii = 0; ; ++ii) {
                int k = K - i + ii * K;
                if (k <= 0) continue;
                if (k > N) break;
                kList.add(k);
            }

                for (int k : kList) {
                    // System.out.println(i + ", " + j + ", " + k);
                    if ((j + k) % K == 0 && (k + i) % K == 0) {
                        cnt++;
                        // System.out.println("t");
                    }
                }
            }
        }

        System.out.print(cnt);
    }
}