数据结构之归并排序

代码出处：https://blog.csdn.net/qq_41174677/article/details/88630180

归并排序的思路就是先两个两个的比较，然后再四个四个的比较，然后再八个八个的比较以此类推。比较完成之后就排序好了。

#include<stdio.h>
#include<stdlib.h>

//将有二个有序数列a[first...mid]和a[mid...last]合并。
void mergearray(int *a, int first, int mid, int last, int *temp)
{
	int i = first, j = mid + 1;
	int m = mid, n = last;
	int k = 0;

	while (i <= m && j <= n)
	{
		if (a[i] <= a[j])
			temp[k++] = a[i++];
		else
			temp[k++] = a[j++];
	}

	while (i <= m)//把i开始没有放进来的数全放进temp
		temp[k++] = a[i++];

	while (j <= n)//
		temp[k++] = a[j++];

	for (i = 0; i < k; i++)//把结果返回给数组a
		a[first + i] = temp[i];
}
void mergesort(int a[], int first, int last, int *temp)
{
	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, last, temp); //再将二个有序数列合并
	}
}

bool MergeSort(int *a, int n)
{
	int *p = (int *)malloc(sizeof(int)*n);
	if (p == NULL)
		return false;
	mergesort(a, 0, n - 1, p);
	delete[] p;
	return true;
}
int main(){
	int a[8] = { 49, 38, 65, 97, 76, 13, 27, 49 };
	MergeSort(a, 8);
	for (int i = 0; i < 8; i++){
		printf("%d\t", a[i]);
	}
	return 0;
}