桶排序

桶排序适用于数据量大, 且分布均匀的情况.

 

程序代码：

package rickgong.algorithm.sort;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

/**
 * Created by rick on 2015/3/8.
 */
public class BucketSortTest {
    public static void main(String[] args) {
        BucketSortTest sortTest = new BucketSortTest();
        int[] array = {84, 32, 87, 24, 67, 52, 85, 13, 53, 48, 21, 95, 98, 21, 45, 12, 75, 72, 54, 62};
        sortTest.printArray(array);
        System.out.println("begin:");

        sortTest.bucketSort(array, 20);
    }

    private void bucketSort(int[] array, int bucketCapacity) {
        //init buckets
        int maxValue = array[0];
        int minValue = array[0];
        for (int i = 0; i < array.length; i++) {
            if (array[i] > maxValue) {
                maxValue = array[i];
            }
            if (array[i] < minValue) {
                minValue = array[i];
            }
        }
        int bucketCount = (int) Math.ceil((maxValue - minValue + 1) * 1.0 / bucketCapacity);
        List<List<Integer>> buckets = new ArrayList<List<Integer>>(bucketCount);
        for (int i = 0; i < bucketCount; i++) {
            buckets.add(i, new ArrayList<Integer>());
        }

        //fill buckets
        System.out.println("fill each bucket");
        for (int i = 0; i < array.length; i++) {
            int bucketIndex = (array[i] - minValue) / bucketCapacity;
            buckets.get(bucketIndex).add(array[i]);

            printBuckets(buckets);
            System.out.println();
        }

        //sort each bucket
        System.out.println("sort each bucket");
        for (int i = 0; i < buckets.size(); i++) {
            Collections.sort(buckets.get(i));
        }

        printBuckets(buckets);
    }

    private void printBuckets(List<List<Integer>> buckets) {
        for (int i = 0; i < buckets.size(); i++) {
            System.out.print("{");
            List<Integer> bkt = buckets.get(i);
            for (int j = 0; j < bkt.size(); j++) {
                System.out.print(bkt.get(j) + "\t");
            }
            System.out.print("}");
        }
    }

    private void printArray(int[] array) {
        for (int i = 0; i < array.length; i++) {
            System.out.print(array[i] + "\t");
        }
        System.out.println();
    }

    private void assertSorted(int[] array) {
        boolean sorted = true;
        for (int i = 0; i < array.length - 1; i++) {
            if (array[i] > array[i + 1]) {
                sorted = false;
                break;
            }
        }
        if (!sorted) {
            throw new RuntimeException("Not sorted");
        }
    }
}

 

输出结果：

84 32 87 24 67 52 85 13 53 48 21 95 98 21 45 12 75 72 54 62
begin:
fill each bucket
{}{}{}{84 }{}
{}{32 }{}{84 }{}
{}{32 }{}{84 87 }{}
{24 }{32 }{}{84 87 }{}
{24 }{32 }{67 }{84 87 }{}
{24 }{32 }{67 52 }{84 87 }{}
{24 }{32 }{67 52 }{84 87 85 }{}
{24 13 }{32 }{67 52 }{84 87 85 }{}
{24 13 }{32 }{67 52 53 }{84 87 85 }{}
{24 13 }{32 48 }{67 52 53 }{84 87 85 }{}
{24 13 21 }{32 48 }{67 52 53 }{84 87 85 }{}
{24 13 21 }{32 48 }{67 52 53 }{84 87 85 }{95 }
{24 13 21 }{32 48 }{67 52 53 }{84 87 85 }{95 98 }
{24 13 21 21 }{32 48 }{67 52 53 }{84 87 85 }{95 98 }
{24 13 21 21 }{32 48 45 }{67 52 53 }{84 87 85 }{95 98 }
{24 13 21 21 12 }{32 48 45 }{67 52 53 }{84 87 85 }{95 98 }
{24 13 21 21 12 }{32 48 45 }{67 52 53 }{84 87 85 75 }{95 98 }
{24 13 21 21 12 }{32 48 45 }{67 52 53 }{84 87 85 75 72 }{95 98 }
{24 13 21 21 12 }{32 48 45 }{67 52 53 54 }{84 87 85 75 72 }{95 98 }
{24 13 21 21 12 }{32 48 45 }{67 52 53 54 62 }{84 87 85 75 72 }{95 98 }
sort each bucket
{12 13 21 21 24 }{32 45 48 }{52 53 54 62 67 }{72 75 84 85 87 }{95 98 }