//合并將兩個(gè)有序序列（[low,mid],[mid+1,high]）合并
void Merge(int arr[],int low,int mid,int high)
{
  int i=low,j=mid+1,p=0;

  int *newarr = (int *)malloc((high-low+1)*sizeof(int));//用來暫存排序好的數(shù)據(jù)
  if(!newarr){
    printf("malloc error!\n");
    exit(1);
  }

  while(i<=mid && j<=high){    //以下過程很類似兩個(gè)有序字符串合并成一個(gè)有序字符串
    if(arr[i] < arr[j])
      newarr[p++] = arr[i++];
    else
      newarr[p++] = arr[j++];
  }

  while(i<=mid)
    newarr[p++] = arr[i++];
  while(j<=high)
    newarr[p++] = arr[j++];

  for(i=low,p=0;p<(high-low+1);i++,p++)  //將結(jié)果復(fù)制到原數(shù)組當(dāng)中
    arr[i] = newarr[p];
  free(newarr);
}

/*
 * File: mergesort.c
 * Time: 2014-07-19 HJJ
 */
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

static void merge1(int array[], int tmp[], int lpos, int rpos, int rend);
static void msort1(int array[], int tmp[], int left, int right);

void merge_sort1(int array[], int n)
{
 assert(array!=NULL && n>1); //條件不滿足，退出程序并打印錯(cuò)誤語(yǔ)句。

 int *tmp = (int *)malloc(sizeof(int) * n);
 assert(tmp != NULL);
 int i;
 for (i = 0; i < n; i ++) {
 tmp[i] = array[i];
 }
 msort1(array, tmp, 0, n-1);

 free(tmp);
}

//遞歸的調(diào)用此函數(shù)，實(shí)現(xiàn)折半劃分，只完成劃分，不實(shí)現(xiàn)排序，最終返回array[]數(shù)組有序
static void msort1(int array[], int tmp[], int left, int right)
{
 assert(array!=NULL && tmp!=NULL);

 if (left == right)
 return;

 int center = (left + right) / 2;
 msort1(tmp, array, left, center);
 msort1(tmp, array, center+1, right);
 merge1(tmp, array, left, center+1, right);
}

//該函數(shù)實(shí)現(xiàn)，將array[]的左右兩半排好序的數(shù)組，歸并為tmp[]，并排序
static void merge1(int array[], int tmp[], int lpos, int rpos, int rend)
{
 assert(array!=NULL && tmp!=NULL);

 int lend = rpos - 1;
 int tmp_pos = lpos;

 while (lpos<=lend && rpos<=rend) {
 if (array[lpos] <= array[rpos])
  tmp[tmp_pos++] = array[lpos++];
 else
  tmp[tmp_pos++] = array[rpos++];
 }

 while (lpos <= lend)
 tmp[tmp_pos++] = array[lpos++];
 while (rpos <= rend)
 tmp[tmp_pos++] = array[rpos++];
}

int main(int argc, char *argv[])
{
  int a[7] = {6, 5, 4, 3, 2, 1, 7};

  merge_sort1(a, 7);
  int i;
  for (i = 0; i < 7; i ++) {
    printf("%3d", a[i]);
  }
  printf("\n");

  return 0;
}

void merge_sort1(int array[], int n)
{
 assert(array!=NULL && n>1); //條件不滿足，退出程序并打印錯(cuò)誤語(yǔ)句。

 int *tmp = (int *)malloc(sizeof(int) * n);
 assert(tmp != NULL);
 int i;
 for (i = 0; i < n; i ++) {
 tmp[i] = array[i];
 }
 msort1(array, tmp, 0, n-1);

 free(tmp);
}

//遞歸的調(diào)用此函數(shù)，實(shí)現(xiàn)折半劃分，只完成劃分，不實(shí)現(xiàn)排序，最終返回array[]數(shù)組有序
static void msort1(int array[], int tmp[], int left, int right)
{
 assert(array!=NULL && tmp!=NULL);

 if (left == right)
 return;

 int center = (left + right) / 2;
 msort1(tmp, array, left, center);
 msort1(tmp, array, center+1, right);
 merge(tmp, array, left, center+1, right);
}

void merge(int array[],int tmp[],int lpos,int rpos,int rend)
{
  int i,leftend,num,tmppos;

  leftend = rpos - 1;
  num = rend - lpos + 1;
  tmppos = lpos;

  while(lpos <= leftend && rpos <= rend){
    if(array[lpos] <= array[rpos])
      tmp[tmppos++] = array[lpos++];
    else
      tmp[tmppos++] = array[rpos++];
  }

  while(lpos <= leftend)
    tmp[tmppos++] = array[lpos++];
  while(rpos <= rend)
    tmp[tmppos++] = array[rpos++];

  for(i = 0;i < num;i++,rend--)
    array[rend] = tmp[rend];
}

/*自底向上，這里就不寫真正的代碼了，從網(wǎng)上copy了*/
void MergePass(SeqList R，int length)
{ //對(duì)R[1..n]做一趟歸并排序
  int i;
  for(i=1;i+2*length-1<=n;i=i+2*length)
    Merge(R,i,i+length-1,i+2*length-1);
  //歸并長(zhǎng)度為length的兩個(gè)相鄰子文件
  if(i+length-1<n) //尚有兩個(gè)子文件，其中后一個(gè)長(zhǎng)度小于length
    Merge(R,i,i+length-1，n)； //歸并最后兩個(gè)子文件
//注意：若i≤n且i+length-1≥n時(shí)，則剩余一個(gè)子文件輪空，無須歸并
} //MergePass

void MergeSort(SeqList R)
{//采用自底向上的方法，對(duì)R[1..n]進(jìn)行二路歸并排序
  int length;
  for(1ength=1;length<n;length*=2) //做 趟歸并
    MergePass(R，length); //有序段長(zhǎng)度≥n時(shí)終止
}

void MSort(int arr[],int low,int high)
{
  if(low < high){
    int mid = (low+high)/2;
    MSort(arr,low,mid);   //左半?yún)^(qū)排序
    MSort(arr,mid+1,high); //右半?yún)^(qū)排序
    Merge(arr,low,mid,high);//左右半?yún)^(qū)合并
  }
}