Selecting random values from an array based on a condition

Question

Hi All,
I have a small glitch here. hope you guys can help me out.
I have an evenly spaced integer array as X[ ] = {1,2,3, ....150}. and I need to create a new array which selects 5 random values from X [ ] , but with a condition that these random values should have a difference of atleast 25 between them.
for example res [ ] = {2,60,37,110,130}
res [ ] = {10,40,109,132,75}
I have been thinking of looping thru the X [ ], and selecting randomly but things look tricky once I sit down to write an algorithm to do it.
Can anyone think of an approach to do this, any help will be greatly appreciated ...

Answer 1

For your interest, here is my attempt.
import java.util.Random;
public class TestDemo {
    public static void main(String[] args) throws Exception {
        for (int n = 0; n < 10; n++) {
            System.out.println(toString(getValues(5, 25, 150)));
    private final static Random RAND = new Random();
    public static int[] getValues(int num, int spread, int max) {
        if (num * spread >= max) {
            throw new IllegalArgumentException("Cannot produce " + num + " spread " + spread + " less than or equals to " + max);
        int[] nums = new int[num];
        int max2 = max - (num - 1) * spread - 1;
        // generate random offsets totally less than max2
        for (int j = 0; j < num; j++) {
            int next = RAND.nextInt(max2);
            // favour smaller numbers.
            if (max2 > spread/2)
                next = RAND.nextInt(next+1);
            nums[j] = next;
            max2 -= next;
        // shuffle the offsets.
        for (int j = num; j > 1; j--) {
            swap(nums, j - 1, RAND.nextInt(j));
        // add the spread of 25 each.
        for (int j = 1; j < num; j++) {
            nums[j] += nums[j-1] + spread;
        return nums;
    private static void swap(int[] arr, int i, int j) {
        int tmp = arr;
arr[i] = arr[j];
arr[j] = tmp;
public static String toString(int[] nums) {
StringBuffer sb = new StringBuffer(nums.length * 4);
sb.append("[ ");
for (int j = 0; j < nums.length; j++) {
if (j > 0) {
sb.append(", ");
sb.append(nums[j]);
sb.append(" ]");
return sb.toString();