Question

We need to generate random numbers within a certain digit range with few restrictions 
e.g. For double digit range 11 - 99, the resultant output should not include all like numbers [11,22,33,44,...99] and multiples of 10 [20,30,40....90]

The resultant output should be [12,13,14,15,16,17,18,19,21,23,...98]

Note: This function should work seamlessly for other digit ranges also (e.g. 3 digit ranges spanning 101 – 999 and four digit ranges spanning 1001 – 9999)

We are having difficulties in identifying like numbers (e.g 11, 22, 33, 44, 55, 66, 77, 88, 99, 111, 222, 333, …., 3333 …)

EDIT1:

protected static List<Integer> fetchRandIntegers(int min, int max, int howMany, boolean randomize) {

    // We need to reverse minimum, maximum values for negative ranges
    if (min > max) {
        int tmp = min;
        min = max;
        max = tmp;
    }

    List<Integer> allNumbers = new ArrayList<Integer>();
    for (int i = min; i <= max; i++) {
        allNumbers.add(i);
    }

    if (randomize) {
    ...
    }

    return allNumbers;

}

Answer 1

To identify if integer i has all digits the same:

• Convert i to string and compare the characters, or
• Repeatedly modulo and divide by 10 and check if all modulos are the same

with something like:

public boolean hasAllDigitsSame (int i)
{
    int a = i ;
    int m = a % 10 ;
    int mm = m ;
    while(a > 0)
    {
        m = a % 10;
        if (m != mm)
          return False ;
        a /= 10 ;
    }
    return True ;
 }

To identify if integer i is a multiple of 10 (100, 1000):

• Check if i modulo 10 is 0.