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 C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)


#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <stack>
#include <queue>
#include <functional>
#include <math.h>
#include <stdlib.h>
#include <map>
#include <deque>
#include <list>
#include <sys/timeb.h>
#include <fstream>
#include <set>

using namespace std;

#define repr(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repr(i,0,n)
#define reprrev(i,a,b) for(int i=(int)(b)-1;i>=(int)(a);i--)
#define reprev(i,n) reprrev(i,0,n)
#define repi(itr,ds) for(auto itr=ds.begin();itr!=ds.end();itr++)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define mp make_pair
#define mt make_tuple
#define INF 1050000000
#define INFL 1100000000000000000LL
#define EPS (1e-10)
#define MOD 1000000007
#define PI 3.1415926536
#define RMAX 4294967295

typedef long long ll;
typedef pair<int, int> Pi;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<bool> vb;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<Pi> vPi;
typedef vector<vector<int> > vvi;
typedef vector<vector<bool> > vvb;
typedef vector<vector<ll> > vvll;
typedef vector<vector<char> > vvc;
typedef vector<vector<string> > vvs;
typedef vector<vector<double> > vvd;
typedef vector<vector<Pi> > vvPi;
typedef priority_queue<int, vector<int>, greater<int> > pqli;
typedef priority_queue<ll, vector<ll>, greater<ll> > pqlll;
typedef priority_queue<Pi, vector<Pi>, greater<Pi> > pqlP;
struct Edge {
	int from, to, cost;
	bool operator<(Edge e) {
		return cost < e.cost;
	}
};
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
template <class T>
using vec = vector<T>;
template<class T>
using pql = priority_queue<T, vector<T>, greater<T>>;
string debug_show(Pi a) {
	return "(" + to_string(a.first) + "," + to_string(a.second) + ")";
}

template<class T>
struct augEdge {
	T from, to;
	int cost;
	bool operator<(augEdge e) { return cost < e.cost; }
	bool operator>(augEdge e) { return cost > e.cost; }
};
template<class T>
using augGraph = vector<augEdge<T>>;


int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int n, m;
	cin >> n >> m;
	ll ans = 0;

	int t1 = (n / m);
	int t2 = (n % m);

	repr(i, 1, m+1) {
		repr(j, i, m+1) {
			if ((i + j) % m != 0) continue;
			repr(k, j, m+1) {
				if ((j + k) % m != 0) continue;

				if ((k + i) % m == 0) {
					int t = 1;
					if (i <= t2) t *= t1+1;
					else t *= t1;
					if (j <= t2) t *= t1+1;
					else t *= t1;
					if (k <= t2) t *= t1+1;
					else t *= t1;

					if (i == j && j == k) {
						ans += 1 * t;
					}
					else if (i == j || j == k || k == i) {
						ans += 3 * t;
					}
					else {
						ans += 6 * t;
					}
				}
			}
		}
	}

	/*
	repr(i,1, n+1) {
		repr(j, i, n+1) {
			if ((i + j) % m != 0) continue;
			repr(k, j, n+1) {
				if ((j + k) % m != 0) continue;

				if ((k + i) % m == 0) {
					if (i == j && j == k) {
						ans += 1;
					}
					else if (i == j || j == k || k == i) {
						ans += 3;
					}
					else {
						ans += 6;
					}
				}

			}
		}
	}
	*/
	cout << ans << endl;

	return 0;
}