Question

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How do you efficiently generate a list of K non-repeating integers between 0 and an upper bound N

What are some alternative methods to generate 1000 distinct random integers in the range [0,8000] as opposed to the following:

1. naive method: generating a number and checking if it’s already in the array. O(n^2)
2. linear shuffle: generate sequence 0 to 8000, shuffle, take the first 1000. O(n)

Answer 1

You can use a partial Fisher-Yates shuffle implemented using swaps. One of the nice features of this algorithm is that if you stop after k swaps, the first k numbers are a random sample of size k from the complete set.