Java中的一些基础算法

/**
 * 插入排序、冒泡排序、选择排序、快速排序
 * @author ZHANGHAOHAO
 * @date 2017/5/10
 */

public class Algorithm {

    /**
     * 插入排序:把未排序的插入到有序的序列里面
     *
     * @param array
     * @return
     */
    public static void insertSort(int[] array) {
        if (array == null || array.length == 0)
            throw new NullPointerException("no sort");
        for (int i = 1; i < array.length; i++) {
            for (int j = 0; j < i; j++) {
                if (array[i] < array[j]) {
                    int temp = array[i];
                    array[i] = array[j];
                    array[j] = temp;
                }
            }
        }
    }

    /**
     * 冒泡排序:把最大的数冒泡到最后面
     *
     * @param array
     * @return
     */
    public static int[] bubbleSort(int[] array) {
        if (array == null || array.length == 0)
            throw new NullPointerException("no sort");
        for (int j = 0; j < array.length - 1; j++) {
            for (int i = 0; i < array.length - j - 1; i++) {
                if (array[i] > array[i+1]) {
                    int temp = array[i];
                    array[i] = array[i+1];
                    array[i+1] = temp;
                }
            }
        }
        return array;
    }

    /**
     * 选择排序： 选出最小的和第一位数交换，选出第二小的和第二位数交换
     *
     * @param array
     * @return
     */
    public static int[] selectSort(int[] array) {
        if (array == null || array.length == 0)
            throw new NullPointerException("no sort");
        for (int j = 0; j < array.length - 1; j++) {
            int min = array[j];
            int n = j;
            for (int i = j + 1; i < array.length; i++) {
                if (array[i] < min) {
                    min = array[i];
                    n = i;
                }
            }
            if (n != j) {
                int temp = array[j];
                array[j] = array[n];
                array[n] = temp;
            }
        }
        return array;
    }

    /**
     * 快速排序，先找到中间值，然后在分块排序
     *
     * @param array
     * @return
     */
    public static int[] fastSort(int[] array, int start, int end) {
        if (array == null || array.length == 0 || end >= array.length)
            throw new NullPointerException("no sort");
        if (end > start) {
            int middle = getMiddle(array, start, end);
            getMiddle(array, start, middle - 1);
            getMiddle(array, middle + 1, end);
        }
        return array;
    }

    public static int getMiddle(int[] array, int start, int end) {
        int middle = array[start];
        while (end > start) {
            while (end > start && array[end] >= middle)
                end--;
            array[start] = array[end];
            while (end > start && array[start] <= middle)
                start++;
            array[end] = array[start];
        }
        array[start] = middle;
        return start;
    }
}