Sorting by Subtraction | 易学教程

问题

So I was working on this sorting algorithm in java, and was wondering if anybody has seen anything like this before. Specifically, this algorithm is meant to sort very large lists with a very small range of numbers. If you have seen that or have any suggestions to enhance the algorithm, can you say something about that below? I have the code here:

public static int[] sort(int[] nums)
{   
    int lowest = Integer.MAX_VALUE;

    for (int n : nums)
    {
        if (n < lowest)
            lowest = n;
    }

    int index = 0;

    int down = 0;

    while (index < nums.length)
    {
        for (int i = index; i < nums.length; i++)
        {
            if (nums[i] == lowest)
            {
                int temp = nums[i] + down;
                nums[i] = nums[index];
                nums[index] = temp;

                index++;
            }
            else 
                nums[i]--;
        }
        down++;
    }

    return nums;
}

回答1:

If I'm not mistaken, that is your standard-issue BubbleSort. It's simple to implement but has poor performance: O(n^2). Notice the two nested loops: as the size of the array increases, the runtime of the algorithm will increase exponentially.

It's named Bubble Sort because the smallest values will "bubble" to the front of the array, one at a time. You can read more about it on Wikipedia.

回答2:

So the algorithm seems to work but it does a lot of unnecessary work in the process.

Basically you are throwing in the necessity to subtract from a number x times before you add x back and try and swap it where x is the difference between the number and the lowest number in the array. Take [99, 1] for example. With your algorithm you would update the array to [98, 1] in the first for loop iteration and then the next you would make the swap [1, 98] then you have to make 97 more iterations to bring your down variable up to 98 and your array to [1,1] state then you add 98 to it and swap it with itself. Its an interesting technique for sure but its not very efficient.

The best algorithm for any given job really depends on what you know about your data. Look into other sorting algorithms to get a feel for what they do and why they do it. Make sure that you walk through the algorithm you make and try to get rid of unnecessary steps.

To enhance the algorithm first I would get rid of finding the lowest in the set and remove the addition and subtraction steps. If you know that your numbers will all be integers in a given range look into bucket sorting otherwise you can try merge or quicksort algorithms.

来源：https://stackoverflow.com/questions/39501191/sorting-by-subtraction

标签

java

sorting