排序算法

1.选择排序

/**
 * 选择排序。
 * 
 * @author daniel
 * @date 2013-12-1 下午8:35:23
 * @since 0.1
 * @version 0.1
 */
public class SelectionSort {
    public static void sel_sort(int x[], int n) {
        for (; n > 1; n--) {//基于数的个数进行循环，每次减少一个数
            int i_max = 0;//i_max用于保存最大元素的下标，首先假设第0个元素最大
            for (int i = 1; i < n; i++) {//循环找前n个数中的最大元素
                if (x[i] > x[i_max])
                    i_max = i;//修改i_max的值，使其一直为最大元素的下标
            }
            //交换x[i_max]和x[n-1]的值
            int temp = x[i_max];
            x[i_max] = x[n - 1];
            x[n - 1] = temp;
        }
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        int a[] = { 8, 3, 4, 3, 2, 5, 6, 7, 3, 5, 5, 5, 9 };
        System.out.println("before sort");
        for (int each : a) {
            System.out.print(each + " ");
        }
        sel_sort(a, a.length);
        System.out.println("\nafter sort");
        for (int each : a) {
            System.out.print(each + " ");
        }
    }
}

 

2.快速排序

/**
 * 快速排序。
 * 
 * @author daniel
 * @date 2013-12-1 下午10:28:12
 * @since 0.1
 * @version 0.1
 */
public class QuickSort {

    static void quick_sort(int x[], int first, int last) {
        if (first < last) {
            int split_point = split(x, first, last);
            quick_sort(x, first, split_point - 1);
            quick_sort(x, split_point + 1, last);
        }
    }

    static int split(int x[], int first, int last) {
        int split_point, pivot;
        pivot = x[first];
        split_point = first;
        for (int unknown = first + 1; unknown <= last; unknown++) {
            if (x[unknown] < pivot) {
                split_point++;
                // 交换x[split_point]与x[unknown]的值
                int t = x[split_point];
                x[split_point] = x[unknown];
                x[unknown] = t;
            }
        }
        // 交换x[first]和x[split_point]的值
        x[first] = x[split_point];
        x[split_point] = pivot;

        return split_point;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        int a[] = { 8, 3, 4, 3, 2, 5, 6, 7, 3, 5, 5, 5, 9 };
        System.out.println("before sort");
        for (int each : a) {
            System.out.print(each + " ");
        }
        quick_sort(a, 0, a.length - 1);
        System.out.println("\nafter sort");
        for (int each : a) {
            System.out.print(each + " ");
        }
    }

}