Java RadixSort
/**
* <html>
* <body>
* <P> Copyright 1994-2018 JasonInternational </p>
* <p> All rights reserved.</p>
* <p> Created on 2018年4月10日 </p>
* <p> Created by Jason</p>
* </body>
* </html>
*/
package cn.ucaner.algorithm.sorts;
import java.util.Arrays;
/**
* Radix sort is a non-comparative integer sorting algorithm that sorts data
* with integer keys by grouping keys by the individual digits which share the
* same significant position and value. A positional notation is required, but
* because integers can represent strings of characters (e.g., names or dates)
* and specially formatted floating point numbers, radix sort is not limited to
* integers.
* <p>
* Family: Bucket.<br>
* Space: 10 Buckets with at most n integers per bucket.<br>
* Stable: True.<br>
* <p>
* Average case = O(n*k)<br>
* Worst case = O(n*k)<br>
* Best case = O(n*k)<br>
* <p>
* NOTE: n is the number of digits and k is the average bucket size
* <p>
* @see <a href="https://en.wikipedia.org/wiki/Radix_sort">Radix Sort (Wikipedia)</a>
* <br>
* @author Justin Wetherell <phishman3579@gmail.com>
*/
public class RadixSort {
private static final int NUMBER_OF_BUCKETS = 10; // 10 for base 10 numbers
private RadixSort() { }
public static Integer[] sort(Integer[] unsorted) {
int[][] buckets = new int[NUMBER_OF_BUCKETS][10];
for (int i = 0; i < NUMBER_OF_BUCKETS; i++)
buckets[i][0] = 1; // Size is one since the size is stored in first element
int numberOfDigits = getMaxNumberOfDigits(unsorted); // Max number of digits
int divisor = 1;
for (int n = 0; n < numberOfDigits; n++) {
int digit = 0;
for (int d : unsorted) {
digit = getDigit(d, divisor);
buckets[digit] = add(d, buckets[digit]);
}
int index = 0;
for (int i = 0; i < NUMBER_OF_BUCKETS; i++) {
int[] bucket = buckets[i];
int size = bucket[0];
for (int j = 1; j < size; j++) {
unsorted[index++] = bucket[j];
}
buckets[i][0] = 1; // reset the size
}
divisor *= 10;
}
return unsorted;
}
private static int getMaxNumberOfDigits(Integer[] unsorted) {
int max = Integer.MIN_VALUE;
int temp = 0;
for (int i : unsorted) {
temp = (int) Math.log10(i) + 1;
if (temp > max)
max = temp;
}
return max;
}
private static int getDigit(int integer, int divisor) {
return (integer / divisor) % 10;
}
private static int[] add(int integer, int[] bucket) {
int size = bucket[0]; // size is stored in first element
int length = bucket.length;
int[] result = bucket;
if (size >= length) {
result = Arrays.copyOf(result, ((length * 3) / 2) + 1);
}
result[size] = integer;
result[0] = ++size;
return result;
}
}