快速排序

package com.test.arithmetic;

import java.util.Arrays;

/**
 * Two point go together, small is left and big is right.
 * Thus the first meet will separate the array to half small and half big.
 * Created by Ryan on 2017/3/25/025.
 */
public class QuickSort {
    public  int count = 0;

    public  int[] sort(int[] source, int low, int high) {
        if (low >= high) {
            return source;
        }
        int first = low;
        int last = high;
        int key = source[first];

        while (first < last) {
            //find the first smaller from the end
            while (last > first && source[last] >= key) {
                last--;
            }
            if (first < last) {
                source[first] = source[last];
                first++; //The first one has already been sorted, move to the next one.
            }//else first = last, that is the same one, do not need to swap them

            //find the first bigger from the start
            while (first < last && source[first] <= key) {
                first++;
            }

            if (first < last) {
                source[last] = source[first];
                last--; //The last one has already been sorted as a bigger, move to the previous one.
            }

        }

        source[first] = key; //put the key
        System.out.println("The " + ++count + " sort:");
        Arrays.stream(source).forEach(item -> System.out.print(item + ", "));
        System.out.println();

        sort(source, low, first - 1);
        sort(source, first + 1, high);
        return source;

    }



    public void quickSort1(int arr[], int low, int high) {
        int l = low;
        int h = high;
        int key = arr[low];

        while (l < h) {
            while (l < h && arr[h] >= key) {
                h--;
            }

            if (l < h) {
                int temp = arr[h];
                arr[h] = arr[l];
                arr[l] = temp;
                l++;
            }

            while (l < h && arr[l] <= key) {
                l++;
            }


            if (l < h) {
                int temp = arr[h];
                arr[h] = arr[l];
                arr[l] = temp;
                h--;
            }
        }
        System.out.print("l=" + (l + 1) + "h=" + (h + 1) + "key=" + key + "\n");
        if (l > low) quickSort1(arr, low, l - 1);
        if (h < high) quickSort1(arr, l + 1, high);
    }


    public <T> void swap(T[] source, int i, int j) {
        T temp = source[i];
        source[i] = source[j];
        source[j] = temp;
    }

    /**
     * 方式2 更高效点的代码：
     */
    public <T extends Comparable<? super T>> T[] quickSort2(T[] targetArr, int start, int end) {
        int i = start + 1, j = end;
        T key = targetArr[start];

        if (start >= end) return (targetArr);

        /**
         * 从i++和j--两个方向搜索不满足条件的值并交换
         *条件为：i++方向小于key，j--方向大于key
         */
        while (true) {
            while (targetArr[j].compareTo(key) > 0) j--;
            while (targetArr[i].compareTo(key) < 0 && i < j) i++;
            if (i >= j) break;
            this.swap(targetArr, i, j);
            if (targetArr[i] == key) {
                j--;
            } else {
                i++;
            }
        }

        /**
         * 关键数据放到‘中间’*
         */
        this.swap(targetArr, start, j);

        if (start < i - 1) {
            this.quickSort2(targetArr, start, i - 1);
        }
        if (j + 1 < end) {
            this.quickSort2(targetArr, j + 1, end);
        }

        return targetArr;
    }

    /**
     * 方式3：减少交换次数，提高效率
     */
    public  <T extends Comparable<? super T>> void quickSort3(T[] targetArr, int start, int end) {
        int i = start, j = end;
        T key = targetArr[start];

        while (i < j) {
                /*按j--方向遍历目标数组，直到比key小的值为止*/
            while (j > i && targetArr[j].compareTo(key) >= 0) {
                j--;
            }
            if (i < j) {
                    /*targetArr[i]已经保存在key中，可将后面的数填入*/
                targetArr[i] = targetArr[j];
                i++;
            }
                /*按i++方向遍历目标数组，直到比key大的值为止*/
                /*此处一定要小于等于零，假设数组之内有一亿个1，0交替出现的话，而key的值又恰巧是1的话，那么这个小于等于的作用就会使下面的if语句少执行一亿次。*/
            while (i < j && targetArr[i].compareTo(key) <= 0) {
                i++;
            }
            if (i < j) {
                    /*targetArr[j]已保存在targetArr[i]中，可将前面的值填入*/
                targetArr[j] = targetArr[i];
                j--;
            }
                /*此时i==j*/
            targetArr[i] = key;

                /*递归调用，把key前面的完成排序*/
            this.quickSort3(targetArr, start, i - 1);

                /*递归调用，把key后面的完成排序*/
            this.quickSort3(targetArr, j + 1, end);
        }
    }


}

package com.test.arithmetic;

import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;

import java.util.Arrays;

import static org.junit.Assert.*;

/**
 * Created by Ryan on 2017/3/25/025.
 */
public class QuickSortTest {
    private int[] source;
    private Integer[] source2;
    private Integer[] source3;
    private QuickSort quick;

    private int[] expect;
    private Integer[] expect2;
    private Integer[] expect3;

    @Before
    public void setUp(){
        source = new int[]{13, 16, 1, 1, 5, 15, 13, 15, 13, 8};
        source2 = new Integer[]{13, 16, 1, 1, 5, 15, 13, 15, 13, 8};
        source3 = new Integer[]{13, 16, 1, 1, 5, 15, 13, 15, 13, 8};

        expect = new int[]{1, 1, 5, 8, 13, 13, 13, 15, 15, 16};
        expect2 = new Integer[]{1, 1, 5, 8, 13, 13, 13, 15, 15, 16};
        expect3 = new Integer[]{1, 1, 5, 8, 13, 13, 13, 15, 15, 16};
        quick = new QuickSort();
    }


    @Test
    public void testSort() throws Exception {
        int[] source = new int[]{13,16,1,1,5,15,13,15,13,8 };
        int[] sort = quick.sort(source, 0, source.length - 1);
        Assert.assertArrayEquals(expect, sort);
    }
    @Test
    public void testSort1(){
        QuickSort quick = new QuickSort();
        quick.quickSort1(source, 0, source.length - 1);
        Assert.assertArrayEquals(expect, source);
    }

    @Test
    public void testSort2(){
        QuickSort quick = new QuickSort();
        quick.quickSort2(source2, 0, source2.length - 1);
        Assert.assertArrayEquals(expect2, source2);
    }
    @Test
    public void testSort3(){
        QuickSort quick = new QuickSort();
        quick.quickSort3(source3, 0, source.length - 1);
        Assert.assertArrayEquals(expect3, source3);
    }

}