计数排序

package algorithm.sort;

public class CountingSort {

    public static void main(String[] args) {

       int[] a = new int[] {5, 3, 7, 2, 1, 4, 9, 8, 6, 1};

       int[] b = sort(a, 9);

       print(b);

    }

    public static int[] sort(int[] a, int k) {

       if (a == null || a.length < 2)

           return a;

       int[] c = new int[k + 1];

       for (int i = 0; i < a.length; i++) {

           c[a[i]] = c[a[i]] + 1;

       }

       for (int i = 1; i < c.length; i++) {

           c[i] = c[i] + c[i - 1];

       }

       int[] b = new int[a.length];

       for (int i = a.length - 1; i >= 0; i--) {

           b[c[a[i]] - 1] = a[i];

           c[a[i]] = c[a[i]] - 1;

       }

       return b;

    }

    public static void exchange(int[] a, int i1, int i2) {

       int tmp = a[i1];

       a[i1] = a[i2];

       a[i2] = tmp;

    }

    public static void print(int[] a) {

       if (a == null || a.length == 0)

           return;

       for (int i = 1; i <= a.length; i++) {

           System.out.print(a[i - 1] + "\t");

           if (i % 5 == 0)

              System.out.println();

       }

    }

}