数据结构与算法之归并排序

归并排序的思想

步骤一：首先将待排序的元素分成大小大致相同的两个序列。
步骤二：再把子序列分成大小大致相同的两个子序列。
步骤三：如此下去，直到分解成一个元素停止，这时含有一个元素的子序列都是有序的。
步骤四：进行合并操作，将两个有序的子序列合并为一个有序序列，如此下去，直到所有的元素都合并为一个有序序列。

归并排序的递归代码实现

void PrintInt(int* ar, int n)
{
	for (int i = 0; i < n; i++)
	{
		printf("%5d", ar[i]);
	}
	printf("\n");
}


void Merge(int* dest, int* src, int left, int mid, int right) //合并
{
	int i = left, j = mid + 1;
	int k = left;
	while (i <= mid && j <= right)
	{
		dest[k++] = src[i] < src[j] ? src[i++] : src[j++];
	}
	while (i <= mid)
	{
		dest[k++] = src[i++];
	}
	while (j <= right)
	{
		dest[k++] = src[j++];
	}
}

void Copy(int* dest, int* src, int left, int right)
{
	for (int i = left; i <= right; i++)
	{
		dest[i] = src[i];
	}
}

void MergePass(int*temp,int*nums,int left, int right)
{
	if (left < right)
	{
		int mid = (right - left) / 2 + left;

		MergePass(temp,nums, left, mid);//先拆分
		MergePass(temp,nums, mid + 1, right);
		Merge(temp,nums, left, mid, right);//合并
		Copy(nums, temp, left, right);
	}
	
}
void MergeSort(int* nums, int n)
{
	if (nullptr == nums || n < 2)return;
	int* temp = new int[n]; //创建一个新的数组
	MergePass(temp,nums, 0, n - 1);
	delete[]temp;
}

int main()
{
	int ar[] = { 56,23,78,45,99,85,12,34,67,100 };
	int n = sizeof(ar) / sizeof(ar[0]);
	MergeSort(ar, n);
	PrintInt(ar, n);
}

归并排序的非递归代码实现

//非递归排序
void PrintInt(int* ar, int n)
{
	for (int i = 0; i < n; i++)
	{
		printf("%5d", ar[i]);
	}
	printf("\n");
}

void Merge(int* dest, int* src, int left, int mid, int right)
{
	int i = left, j = mid + 1;
	int k = left;
	while (i <= mid && j <= right)
	{
		dest[k++] = src[i] < src[j] ? src[i++] : src[j++];
	}
	while (i <= mid)
	{
		dest[k++] = src[i++];
	}
	while (j <= right)
	{
		dest[k++] = src[j++];
	}
}

void MergePass(int* dest, int* src, int n, int s)
{
	int i = 0;
	printf("%d\n", s);
	while (i + 2 * s - 1 <= n-1)
	{
		Merge(dest, src, i, i + s - 1, i + 2 * s - 1);
		printf("left:%d mid:%d right:%d\n", i, i + s - 1, i + 2 * s - 1);
		i = i + 2 * s;
	}
	if (s+i<n)   //n-1>=s+i
	{
		Merge(dest, src, i, i + s - 1, n - 1);
		printf("left:%d mid:%d right:%d\n", i, i + s - 1, n-1);
	}
	else
	{
		for (int j = i; j < n; j++)
		{
			dest[j] = src[j];
		}
	}
}
//以2的次幂方式进行合并
void MergeSort(int* nums, int n)
{
	int* temp = new int[n];
	int s = 1;
	while (s < n)
	{
		MergePass(temp, nums, n, s);
		s += s;
		MergePass(nums, temp, n, s);
		s + s;
	}
	delete[]temp;
}


int main()
{
	int ar[] = { 56,23,78,45,99,85,12,34,67,100 };
	int n = sizeof(ar) / sizeof(ar[0]);
	MergeSort(ar, n);
	PrintInt(ar, n);
}