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## 归并排序算法

Wu Yudong    July 26, 2016     Algorithm   632

1. 申请空间，使其大小为两个已经排序序列之和，该空间用来存放合并后的序列
2. 设定两个指针，最初位置分别为两个已经排序序列的起始位置
3. 比较两个指针所指向的元素，选择相对小的元素放入到合并空间，并移动指针到下一位置
4. 重复步骤3直到某一指针到达序列尾
5. 将另一序列剩下的所有元素直接复制到合并序列尾

// Completed on 2014.10.11 17:20
// Language: C99
//
// 版权所有（C）wuyudong
// 博客地址：http://www.wuyudong.com
#include<stdio.h>
#include<stdlib.h>
void merge_sort(int *list, const int first, const int last)
{
int len= last-first+1;
int left_min,left_max;    //左半区域边界
int right_min,right_max;  //右半区域边界
int index;
int i;
int *tmp;
tmp = (int *)malloc(sizeof(int)*len);
if( tmp == NULL || len <= 0 )
return;

for( i = 1; i < len; i *= 2 )
{
for( left_min = 0; left_min < len - i; left_min = right_max)
{
int j;
right_min = left_max = left_min + i;
right_max = left_max + i;
j = left_min;
if ( right_max > len )
right_max = len;
index = 0;
while( left_min < left_max && right_min < right_max )
{
tmp[index++] = (list[left_min] > list[right_min] ? list[right_min++] : list[left_min++]);
}
while( left_min < left_max )
{
list[--right_min] = list[--left_max];
}
while( index > 0 )
{
list[--right_min] = tmp[--index];
}
}
}
free(tmp);
}
int main()
{
int a[] = {288, 52, 123, 30, 212, 23, 10, 233};
int n, mid;
n = sizeof(a) / sizeof(a[0]);
mid = n / 2;
merge_sort(a, 0, n - 1);
for(int k = 0; k < n; k++)
printf("%d ", a[k]);
printf("\n");
return 0;
}

void merge(int *array,const int first, const int mid, const int last)
{
int i,index;
int first1,last1;
int first2,last2;
int *tmp;
tmp = (int *)malloc((last-first+1)*sizeof(int));
if( tmp == NULL )
return;
first1 = first;
last1  = mid;
first2 = mid+1;
last2  = last;
index = 0;
while( (first1 <= last1) && (first2 <= last2) )
{
if( array[first1] < array[first2] )
{
tmp[index++] = array[first1];
first1++;
}
else{
tmp[index++] = array[first2];
first2++;
}
}
while( first1 <= last1 )
{
tmp[index++] = array[first1++];
}
while( first2 <= last2 )
{
tmp[index++] = array[first2++];
}
for( i=0; i<(last-first+1); i++)
{
array[first+i] = tmp[i];
}
free(tmp);
}
void merge_sort(int *array, const int first, const int last)
{
int mid = 0;
if(first < last)
{
mid = (first + last) / 2;
merge_sort(array, first, mid);
merge_sort(array, mid + 1, last);
merge(array, first, mid, last);
}
}