小白也能看懂的归并排序！！！

#include<iostream>
using namespace std;
#include<algorithm>
//合并两个有序数组
void MemeryArray(int a[],int la,int b[],int lb,int c[])
{
	int i=0, j=0, k=0;
	while (i < la && j < lb)
	{
		if (a[i] < b[j])
			c[k++] = a[i++];
		else
			c[k++] = b[j++];
	}
	while(i < la)
		c[k++] = a[i++];
	while (j < lb)
		c[k++] = b[j++];
}
void test()
{
	int a[] = { 1,5,8 };
	int b[] = { 2,3,6,10,12 };
	int c[8];
	MemeryArray(a, 3, b, 5,c);
	for_each(c, c + 8, [](int val) {cout << val << " "; });
}
int main()
{
	test();
	return 0;
}

#include<iostream>
using namespace std;
#include<algorithm>
//合并两个有序序列
void mergearray(int a[], int first, int mid, int last, int temp[])
{
	int i =first, j = mid+1, k = 0;
	while (i <=mid && j <=last)
	{
		if (a[i] < a[j])
			temp[k++] = a[i++];
		else
			temp[k++] = a[j++];
	}
	while (i <=mid)
	{
		temp[k++] = a[i++];
	}
	while (j <=last)
	{
		temp[k++] = a[j++];
	}
	//最后把temp里面存放的合并后为有序的左右序列倒回原数组a
	//注意a的起点
	for (int i = 0; i < k; i++)
	{
		a[first+i] = temp[i];
	}
}
//拆分数组，有序合并
void mergesort(int a[],int first,int last,int temp[])
{
	//没有拆分到只剩一个元素的极小序列
	if(first < last)
	{
		int mid = (first + last) / 2;
		mergesort(a, first, mid, temp);//拆分左边序列，合并为有序序列
		mergesort(a, mid + 1, last, temp);//拆分右边序列，合并为有序序列
		mergearray(a, first, mid, last, temp);//将左序列和右序列合并为一整个有序序列
	}
}
//归并排序主函数
void MergeSort(int a[],int n)
{
	int* p = new int[n];
	if (!p)
		return;
	mergesort(a,0,n-1,p);
	delete[] p;
}
void test()
{
	int a[] = { 1,3,5,2,7,9,10 };
	MergeSort(a, 7);
	for_each(a, a + 7, [](int val) {cout << val << " "; });
}
int main()
{
	test();
	return 0;
}

#include<iostream>
using namespace std;
#include<algorithm>
//合并两个有序序列
void mergearray(int a[], int first, int mid, int last, int temp[])
{
	int i =first, j = mid+1, k = 0;
	while (i <=mid && j <=last)
	{
		if (a[i] < a[j])
			temp[k++] = a[i++];
		else
			temp[k++] = a[j++];
	}
	while (i<=mid)
	{
		temp[k++] = a[i++];
	}
	while (j <=last)
	{
		temp[k++] = a[j++];
	}
	//最后把temp里面存放的合并后为有序的左右序列倒回原数组a
	//注意a的起点
	for (int i = 0; i < k; i++)
	{
		a[first+i] = temp[i];
	}
}
//拆分数组，有序合并
void mergesort(int a[],int first,int last,int temp[])
{
	//迭代的实现是直接从最小子序列(含一个元素)开始往上两两合并
	int k = 1;//子序列长度
	int Last=0;
	int First=0;
	int mid=0;
	while (k<last)
	{
		First =0;
		//3.剩余大于等于两个子序列的元素个数
		while (First<=last-2*k+1)//加一的原因是因为下标从0算起
		{
			mid = First + k - 1;
		     Last = First + 2 * k - 1;
			mergearray(a, First, mid, Last, temp);
			First += 2 * k;
		}
		//当剩下的没有合并处理过的元素数量不足2k，即无法构成两个子序列进行合并操作时，要分类处理
	   //1.剩下小于等于一个子序列的元素个数
		if (last-First<=k)
		{
			mid = First + (last - First) / 2;
			mergearray(a, First, mid, last, temp);
		}
		//2.剩下大于一个小于两个的子序列元素个数
		else
		{
			mid = First + k - 1;;
			mergearray(a,First, mid, last, temp);
		}
		k *= 2;
	}
	//说明此时是特殊奇数情况，数组末尾还单着一个元素没有于前面一个完整的子序列合并
	if (First==last)
	{
		mergearray(a, first, last - 1, last, temp);
	}
}
//归并排序主函数
void MergeSort(int a[],int n)
{
	int* p = new int[n];
	if (!p)
		return;
	mergesort(a,0,n-1,p);
	delete[] p;
}
void test()
{
	int a[] = { 3,4,5,6,1,2,7,9,32,6,89,0,5,21,56,22,0,3,1};
	MergeSort(a,19);
	for_each(a, a+19, [](int val) {cout << val << " "; });
}
int main()
{
	test();
	return 0;
}