Generate Unique 4-digit random number without using Random class

Question

I need help in generating a 4-digit random number between 1-8 without using the random class OR the collections.shuffle().

Thanks in advance.

Answer 1

This is one way you can do it:

• Generate an array of 0 - 9.
• Randomly shuffle the array.
• Pick the first four element from the array to construct the 4-digit number.

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int[] nums = {0,1,2,3,4,5,6,7,8,9};

//Shuffle array
for(int x=0; x<nums.length; x++){
    int i = (int)(Math.random()*10);  //generate random 0-9
    int temp = nums[x];
    nums[x] = nums[i];
    nums[i] = temp;
}

From the shuffled array, simply get the first 4 elements and construct your unique number.