Java-四种面试常考排序

快速排序

快速排序的思想依据是分治法，选取第一个元素为对比值，然后将表中比对比值小的放在左边，将对比值大的放在右边，然后再将左边的列表用同样的方法进行排列，将右边的方法进行排列，依次递归下去，最终有序。下面列出java实现

package arithmetic;

/**
 * Created by elijahliu on 2017/3/2.
 */
public class QuickSort {
    int a[] = {49,37,65,97,76,13,27,49,78};

    public QuickSort(){

        quickSort(a,0,a.length-1);

        for (int i:a
             ) {
            System.out.print(i+" ");

        }


    }
    public int getMiddle(int[] list,int low,int high){
        int temp = list[low];
        while (low < high) {
            while (low < high && list[high] >= temp) {
                high--;
            }
            list[low] = list[high];
            while (low < high && list[low] <= temp) {
                low++;
            }
            list[high] = list[low];
        }
        list[low] = temp;
        return low;
    }

    public void _quickSort(int[] list, int low, int high) {

        if (low < high) {
            int mid = getMiddle(list, low, high);
            _quickSort(list, low, mid - 1);
            _quickSort(list, mid + 1, high);
        }
    }

    public void quickSort(int[] list, int low, int high) {
        if (list.length > 0) {
            _quickSort(list, low, high);
        }
    }

    public static void main(String[] args) {
        new QuickSort();
    }

}

直接插入排序

直接插入排序的算法思想：从第二个元素开始，如果比前面的元素都小，那么就将前面的元素往后移一位，然后把自己的值放到前面的位置上，最终由小到大排列。
java实现

package arithmetic;

/**
 * Created by elijahliu on 2017/3/2.
 */
public class InsertSort {
    public InsertSort(){
        insertSort();

    }

    int a[] = {49, 38, 65, 97, 76, 13, 27, 49};

    public void insertSort(){
        int temp = 0;
        for(int i = 1;i=0&&temp

冒泡排序

最简单的冒泡排序，大一就学过了

package arithmetic;

/**
 * Created by elijahliu on 2017/3/2.
 */
public class BubbleSort {

    public BubbleSort() {
        bubbleSort();
    }

    int a[] = {49, 38, 65, 97, 76, 13};

    public void bubbleSort() {
        int temp = 0;
        for (int i = 0; i < a.length - 1; i++) {
            for (int j = 0; j < a.length - 1 - i; j++) {
                if (a[j] > a[j + 1]) {
                    temp = a[j];
                    a[j] = a[j + 1];
                    a[j + 1] = temp;
                }
            }
        }

        for (int i : a
                ) {
            System.out.println(i + "");

        }
    }

    public static void main(String[] args) {
        new BubbleSort();
    }

}

简单选择排序

算法思想：选取第一个作为标准值，然后对比后面的数，选取一个最大的，与第一个进行交换，position用于标记最大的数的位置。然后选择第二个数为标准值，然后依次进行下去。

package arithmetic;

/**
 * Created by elijahliu on 2017/3/2.
 */
public class SelectSort {
    int a[] = {1, 54, 6, 3, 78, 34, 12, 45};

    public SelectSort() {
        seletctSort();
    }

    public void seletctSort() {
        int position = 0;
        for (int i = 0; i < a.length; i++) {
            position = i;
            int temp = a[i];
            for (int j = i + 1; j < a.length; j++) {
                if (a[j] > temp) {
                    temp = a[j];
                    position = j;
                }
            }
            a[position] = a[i];
            a[i] = temp;
        }

        for (int i : a
                ) {
            System.out.print(i + " ");
        }

    }

    public static void main(String[] args) {
        new SelectSort();

    }
}