三大面试排序的归并以及递归实现--快速排序、归并排序、堆排序-优快云博客

本文链接：https://blog.youkuaiyun.com/zhanglu_1024/article/details/76704587

本文详细介绍了三种常用的排序算法——快速排序、归并排序和堆排序的实现方法。不仅提供了递归实现方式，还展示了如何使用循环来实现这些算法。通过具体的代码示例，帮助读者深入理解每种排序算法的工作原理。

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本文主要是三大常用排序的实现，包括快速排序的递归方法，循环方法。归并排序的递归方法，循环方法。以及堆排序。

快速排序：

递归实现（快排）

void Show(int ar[],int len)
{
	copy(ar,ar+len,ostream_iterator<int>(cout," "));
	cout<<endl;
}
//快速排序--递归
int Quick_sort_once(int ar[],int left,int right)
{
	int tmp = ar[left];
	while(left < right)
	{
		while(left < right && tmp <= ar[right])
			right--;
		if(left < right)
			ar[left] = ar[right];
		while(left < right && tmp >= ar[left])
			left++;
		if(left < right)
			ar[right] = ar[left];
	}
	ar[left] = tmp;
	return left;
}
void Quick_sort(int ar[],int left,int right)
{
	if(left < right)
	{
		int mid = Quick_sort_once(ar,left,right);
		Quick_sort(ar,left,mid-1);
		Quick_sort(ar,mid+1,right);
	}
}

void Quick_sort(int ar[],int len)
{
	if(ar == NULL || len <= 0)
		return ;
	Quick_sort(ar,0,len-1);//递归
}

void main()

	int ar[] = {3,6,8,2,4,1,0,9,5};
	int len = sizeof(ar)/sizeof(ar[0]);


	Quick_sort(ar,len);
	Show(ar,len);

循环实现（快排）

int Quick_sort_once(int ar[],int left,int right)
{
	int tmp = ar[left];
	while(left < right)
	{
		while(left < right && tmp <= ar[right])
			right--;
		if(left < right)
			ar[left] = ar[right];
		while(left < right && tmp >= ar[left])
			left++;
		if(left < right)
			ar[right] = ar[left];
	}
	ar[left] = tmp;
	return left;
}

void Quick_sort_while(int ar[],int left,int right)
{
	int *br = new int[(right+1)*2];
	if(br != NULL)
	{
		int count = 0;
		br[count++] = left;
		br[count++] = right;

		while(count > 0)
		{
			int low = br[count-2];
			int high = br[count-1];
			
			if(low < high)
			{
				int mid = Quick_sort_once(ar,low,high);
				count -= 2;
				br[count++] = low;
				br[count++] = mid-1;
				br[count++] = mid+1;
				br[count++] = high;
			}
			else
				count -= 2;
		}
	}
	delete []br;
}
void Quick_sort(int ar[],int len)
{
	if(ar == NULL || len <= 0)
		return ;
	Quick_sort_while(ar,0,len-1);//循环
}

void main()

	int ar[] = {3,6,8,2,4,1,0,9,5};
	int len = sizeof(ar)/sizeof(ar[0]);


	Quick_sort(ar,len);
	Show(ar,len);

归并排序

递归实现（归并）

void Merge_sort_once(int ar[],int br[],int low1,int high1,int low2,int high2)
{
	int k = low1;
	int m = k;
	while(low1 <= high1 && low2 <= high2)
	{
		if(ar[low1] <= ar[low2])
			br[k++] = ar[low1++];
		else
			br[k++] = ar[low2++];
	}
	while(low1 <= high1)
		br[k++] = ar[low1++];
	while(low2 <= high2)
		br[k++] = ar[low2++];
	k--;
	while(k >= m)
		ar[k] = br[k--];
}
void Merge_sort(int ar[],int br[],int left,int right)
{
	if(left < right)
	{
		int mid = left + (right - left) / 2;
		Merge_sort(ar,br,left,mid);
		Merge_sort(ar,br,mid+1,right);
		Merge_sort_once(ar,br,left,mid,mid+1,right);
	}
}

void Merge_sort(int ar[],int len)
{
	if(ar == NULL || len <= 0)
		return ;
	int *br = new int[len+1];
	Merge_sort(ar,br,0,len-1);
}
void main()
{
	int ar[] = {3,6,8,2,4,1,0,9,5};
	int len = sizeof(ar)/sizeof(ar[0]);

	Merge_sort(ar,len);

	Show(ar,len);
}


		循环实现（归并）
void Merge_sort_once(int ar[],int br[],int len,int gap)
{
	int low1 = 0;
	int high1 = low1+gap-1;
	int low2 = high1+1;
	int high2 = low2+gap-1 > len ? len : low2+gap-1;

	int k = 0;
	while(low2 <= len)
	{
		while(low1 <= high1 && low2 <= high2)
		{
			if(ar[low1] <= ar[low2])
				br[k++] = ar[low1++];
			else
				br[k++] = ar[low2++];
		}
		while(low1 <= high1)
			br[k++] = ar[low1++];
		while(low2 <= high2)
			br[k++] = ar[low2++];
		low1 = high2+1;
		high1 = low1+gap-1;
		low2 = high1+1;
		high2 = low2+gap-1 > len ? len : low2+gap-1;
	}
	while(low1 <= len)
		br[k++] = ar[low1++];
	k--;
	while(k >= 0)
	{
		ar[k] = br[k--];
	}
}
void Merge_sort_while(int ar[],int left,int right)
{
	int *br = new int[right+1];
	for(int i = 1; i < right+1; i *= 2)
	{
		Merge_sort_once(ar,br,right,i);
	}
	delete []br;
}

void Merge_sort(int ar[],int len)
{
	if(ar == NULL || len <= 0)
		return ;
	Merge_sort_while(ar,0,len-1);
}
void main()
{
	int ar[] = {3,6,8,2,4,1,0,9,5};
	int len = sizeof(ar)/sizeof(ar[0]);

	Merge_sort(ar,len);
	Show(ar,len);
}

堆排序

void Adjust(int ar[],int k,int len)
{
	int tmp = ar[k];
	int i = k*2+1;
	while(i < len)
	{
		if(i + 1 < len && ar[i] < ar[i+1])
		{
			i++;
		}
		if(ar[i] > tmp)
		{
			ar[k] = ar[i];
			k = i;
			i = k*2+1;
		}
		else
			break;
	}
	ar[k] = tmp;
}
void Heap_sort(int ar[],int len)
{
	if(ar == NULL || len <= 0)
		return ;
	int i = (len-1-1)/2;
	while(i >= 0)
	{
		Adjust(ar,i,len);
		i--;
	}
	for(int k = len-1; k > 0; --k)
	{
		int tmp = ar[0];
		ar[0] = ar[k];
		ar[k] = tmp;
		Adjust(ar,0,k);
	}
}
void main()
{
	int ar[] = {3,6,8,2,4,1,0,9,5};
	int len = sizeof(ar)/sizeof(ar[0]);

	Heap_sort(ar,len);
	Show(ar,len);
}