归并排序及其非递归实现

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目录

归并排序递归实现

归并排序非递归实现

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归并排序递归实现

图示：

代码：

先分再归并，像是后序一般。

//归并排序
void MergeSort(int* arr, int left, int right)
{
 
	int* temp = (int*)malloc(sizeof(int) * (right));
	if (temp == NULL)
	{
		perror("malloc fail");
	}
 
	_MergeSort(arr, temp, left, right - 1);
	free(temp);
}
 
void _MergeSort(int* arr, int* temp, int left, int right)
{
	if (left >= right)
		return;
 
	int mid = (left + right) / 2;
 
	int begin1 = left;
	int begin2 = mid + 1;
	int end1 = mid;
	int end2 = right;
 
	_MergeSort(arr, temp, left, mid);
	_MergeSort(arr, temp, mid + 1, right);
 
	int index = left;
	while (begin1 <= end1 && begin2 <= end2)
	{
		if (arr[begin1] < arr[begin2])
		{
			temp[index++] = arr[begin1++];
		}
		else
		{
			temp[index++] = arr[begin2++];
		}
	}
 
	while (begin1 <= end1)
	{
		temp[index++] = arr[begin1++];
	}
 
	while (begin2 <= end2)
	{
		temp[index++] = arr[begin2++];
	}
 
	memcpy(arr + left, temp + left, sizeof(int) * (right - left + 1));
}

归并排序非递归实现

这里的非递归实现不可借助栈实现，因为返回去的时候，不能使之有序。

代码：

//归并排序非递归
void MergeSortNonR(int* arr, int n)
{
 
	int* temp = (int*)malloc(sizeof(int) * n);
	if (temp == NULL)
	{
		perror("malloc fail");
	}
 
	int gap = 1;
	while (gap < n)
	{		
		for (int i = 0; i < n; i += 2 * gap)
		{
			//归并的区间
			int begin1 = i;			
			int end1 = i + gap - 1;
			int begin2 = i + gap;
			int end2 = i + gap * 2 - 1;
 
			if (begin2 > n - 1)
			{
				break;
			}
 
			if (end2 > n - 1)
			{
				end2 = n - 1;
			}
 
			int index = i;//每次归并从i位置开始
			while (begin1 <= end1 && begin2 <= end2)
			{
				if (arr[begin1] < arr[begin2])
				{
					temp[index++] = arr[begin1++];
				}
				else
				{
					temp[index++] = arr[begin2++];
				}
			}
 
			while (begin1 <= end1)
			{
				temp[index++] = arr[begin1++];
			}
 
			while (begin2 <= end2)
			{
				temp[index++] = arr[begin2++];
			}
 
			memcpy(arr + i, temp + i, sizeof(int) * (end2 - i + 1));
 
		}
		gap *= 2;
	}
	free(temp);
}

时间复杂度O(n*logn),空间复杂度O(N);