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This article mainly introduces "how to realize the java bitmap sorting algorithm". In the daily operation, I believe many people have doubts about how to realize the java bitmap sorting algorithm. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts of "how to realize the java bitmap sorting algorithm". Next, please follow the editor to study!

Algorithm requirement

Input: a file containing up to n positive integers, where each number is less than n (n = 10 ^ 7). There are no duplicate files.

Output: output in ascending order

Constraints: only about 1m of memory space, enough disk space. The maximum run is a few minutes, and if it is 10 seconds, there is no need for optimization.

When I first graduated from school, I was asked by three interviewers about this question. At that time, my first answer was a simple bubble sort. The interviewer directly reminded me that memory was limited, and then I had an idea. I could use a third-party database to store it in the database first, and then query it in order by order. Obviously, this is not a solution. Of course, I didn't answer the question at that time. But now, in retrospect, there is still a solution.

Analysis of problems

If we say that it is obviously unrealistic to introduce this data into memory for sorting, because some of the sizes of n may be more than 1m, we can consider using bitmap sorting.

Implementation summary

Suppose we have a set of data less than 10, such as {3, 1, 1, 8, 5, 4, 9}. We can represent this collection with the following string

0 1 0 1 1 1 0 0 11 where the data in the representative set is represented as 1 and the other is zero

If we use pseudo code, we can do this as follows:

1 initialize an array of size n

For n = [1Jing n]

Bit [I] = 0

2 read every number in each file sequentially

For each i

Bit [I] = 1

3 output

For n = [0jinn)

If (bit [I] = = 1)

Print i

Java code implementation

Int [] arrs = {122.34 arrs = 13Jing 1Jing 143J 321J 1411}; / / Files on disk

Int [] sorts = new int [2000]

For (int arr: arrs) {

Sorts [arr] = 1

}

For (int iTuno Bandi)

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