归并排序:归并算法应用到分治策略,简单说就是把一个答问题分解成易于解决的小问题后一个个解决,最后在把小问题的一步步合并成总问题的解。这里的排序应用递归来把数组分解成一个个小数组,直到小数组的数位有序,在把有序的小数组两两合并而成有序的大数组。
#include<stdio.h>
#include <stdio.h>
#include <stdlib.h>
#define N 7
void merge(int arr[], int low, int mid, int high)
{
int i, k;
int *tmp = (int *)malloc((high - low + 1) * sizeof(int));
//申请空间,使其大小为两个
int left_low = low;
int left_high = mid;
int right_low = mid + 1;
int right_high = high;
for (k = 0; left_low <= left_high && right_low <= right_high; k++)
{
// 比较两个指针所指向的元素
if (arr[left_low] <= arr[right_low])
{
tmp[k] = arr[left_low++];
}
else
{
tmp[k] = arr[right_low++];
}
}
if (left_low <= left_high)
{
//若第一个序列有剩余,直接复制出来粘到合并序列尾
//memcpy(tmp+k, arr+left_low, (left_high-left_low+l)*sizeof(int));
for (i = left_low; i <= left_high; i++)
tmp[k++] = arr[i];
}
if (right_low <= right_high)
{
//若第二个序列有剩余,直接复制出来粘到合并序列尾
//memcpy(tmp+k, arr+right_low, (right_high-right_low+1)*sizeof(int));
for (i = right_low; i <= right_high; i++)
tmp[k++] = arr[i];
}
for (i = 0; i < high - low + 1; i++)
{
arr[low + i] = tmp[i];
}
free(tmp);
return;
}
void merge_sort(int arr[], unsigned int first, unsigned int last) {
int mid = 0;
if (first<last) {
mid = (first + last) / 2; /* 注意防止溢出 */
/*mid = first/2 + last/2;*/
//mid = (first & last) + ((first ^ last) >> 1);
merge_sort(arr, first, mid);
merge_sort(arr, mid + 1, last);
merge(arr, first, mid, last);
}
return;
}
int main() {
int i;
int a[N] = {
32,12,56,78,76,45,36 };
printf("排序前 \n");
for (i = 0; i<N; i++)
printf("%d\t", a[i]);
merge_sort(a, 0, N - 1); // 排序
printf("\n 排序后 \n");
for (i = 0; i<N; i++)
printf("%d\t", a[i]); printf("\n");
system("pause");
return 0;
}