合并排序

  1）把0~length-1的数组分成左数组和右数组
  2）对左数组和右数组进行迭代排序
  3）将左数组和右数组进行合并，那么生成的整个数组就是有序的数据数组(关键)

 

#include <stdio.h>
#include <assert.h>
#include <string.h>
#include <malloc.h>

void merge(int *array, int start, int middle, int end)
{
    int left = start;
    int right = middle + 1;
    int length = end - start + 1;
    int *p = malloc(sizeof(int) * length);
    assert(NULL != p);
    int index = 0;
    int i;
    while(index < length)
    {
        while(left <= middle && right <= end)
        {
            if(array[left] <= array[right])
            {
                p[index] = array[left];
                left ++;
                index ++;
            }
            else
            {
                p[index] = array[right];
                index ++;
                right ++;
            }
        }
        while(left <= middle)
        {
            p[index] = array[left];
            left ++;
            index ++;
        }
        while(right <= end)
        {
            p[index] = array[right];
            index ++;
            right ++;
        }
    }
    for(i = 0; i < length; i ++)
        printf("%d,", p[i]);
    printf("\n");
    memmove(array + start, p, length * sizeof(int));
}

void _merge_sort(int *array, int start, int end)
{
    int middle = start + ((end - start) >> 1);
    if(start >= end)
        return;
    _merge_sort(array, start, middle);
    _merge_sort(array, middle + 1, end);
    merge(array, start, middle, end);
}

void merge_sort(int *array, int length)
{
    assert(NULL != array || 0 != length);
    _merge_sort(array, 0, length - 1);
}


void test()
{
    int i;
    int array[10] = {1,3,4,5,8,6,7,9,0,2};
    merge_sort(array, 10);
    for(i = 0; i < 10; i ++)
    {
        printf("%d, ", array[i]);
    }
    printf("\n");
}

int main()
{
    test();
}