归并排序

归并排序：

                花了几个小时，终于弄懂了 - -!

                一、首先归并排序由分为两步“归”和“并”，“归”是利用递归的方法将原来的无序数组分为若干个单位唯一的子数组，“并”是将原来分成排好序的子表，然后调用 Merger  对子表进行归并，使之成为有序表。

               

       void mergearray(int a[],int m,int b[],int n,int c[])                                    //将子数组进行排序
     {
               int i,j,k;
               i=j=k=0;
               while(i<m && j<n)
               {
                if(a[i]<b[j])
                 c[k++]=a[i++];
                else
                 c[k++]=b[j++];
               }
               while(i<m)
               {
                c[k++]=a[i++];                                                 //从左半数组复制到临时空间                                                                                      
              }
               while(j<n)
               {
                c[k++]=a[j++];                                                 //从右半数组复制到临时空间
           }
               for(i=0;i<k;i++)
                a[i]=c[i];                                                           //从辅助空间复制回a数组
   }
        void mergesort(int a[], int first, int last, int temp[])                                       //递归
       {
               if (first < last)
               {
                int mid = (first + last) / 2;
                mergesort(a, first, mid, temp);    //左边有序
                mergesort(a, mid + 1, last, temp); //右边有序
                mergearray(a+first, mid-first+1, a+mid+1, last-mid, temp); //再将二个有序数列合并
               }
       }

       void main()
       {
               int a[6]={4,1,9,8,2,6};
               int* p = (int*)malloc(sizeof(int)*6);
               mergesort(a,0,5,p);
               for(int i=0;i<6;i++)
                printf("%d ",a[i]);
               free(p);
       }

参考博客： http://blog.youkuaiyun.com/morewindows/article/details/6678165/

                  http://www.cnblogs.com/jillzhang/archive/2007/09/16/894936.html