let's get multiple coprime with combinations and divisors.

MultiCoprime.java

package org.srkim.test;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * let's get multiple coprime with combinations and divisors.
 * 
 * @author srkim
 *
 */
public class MultiCoprime {

	private static List<List<Integer>> list = new ArrayList<List<Integer>>();

	private static int[] nums = { 3, 5, 6, 9, 11 };

	public static void main(String[] args) {
		int size = nums.length;

		for (int i = 0; i < size; i++) {
			getDivisors(nums[i]);
		}
		for (int i = 2; i <= size; i++) {
			combination(new int[size], 0, size, i, 0);
		}

	}

	public static void getDivisors(int num) {

		// add divisors except 1
		List<Integer> result = new ArrayList<Integer>();
		for (int i = 2; i <= num / 2; i++) {
			if (num % i == 0) {
				result.add(i);
			}
		}
		result.add(num);
		list.add(result);
	}

	public static void multiCoprime(int[] arr, int length) {
		int totalSize = 0;
		Set<Integer> setList = new HashSet<Integer>();
		for (int i = 0; i < length; i++) {
			List<Integer> imsiList = list.get(arr[i]);
			totalSize += imsiList.size();
			System.out.println(imsiList.get(imsiList.size() - 1) + "'s set : " + imsiList);
			setList.addAll(imsiList);
		}

		for (int i = 0; i < length; i++)
			System.out.print(nums[arr[i]] + " ");

		if (totalSize == setList.size()) {
			System.out.println("==> coprime");
		} else {
			System.out.println("==> not coprime");
		}
		System.out.println();
	}

	public static void combination(int[] arr, int index, int n, int r, int target) {
		if (r == 0)
			multiCoprime(arr, index);
		else if (target == n)
			return;
		else {
			arr[index] = target;
			combination(arr, index + 1, n, r - 1, target + 1);
			combination(arr, index, n, r, target + 1);
		}
	}
}