C语言超详细讲解排序算法下篇

void BubbleSort(int* a, int n)//升序
{
	//时间复杂度O(N^2)
	while (n > 0)
	{
		int exchange = 0;
		for (int i = 1; i < n; ++i)//防止越界访问
		{
			if (a[i - 1] > a[i])
			{
				Swap(&a[i - 1], &a[i]);//交换
				exchange = 1;
			}
		}
		if (exchange == 0)
		{
			break;
		}
		--n;
	}
}

void QuickSort(int* a, int left, int right)//升序
{
	if (left >= right)
	{
		return;
	}
 
	int begin = left;
	int end = right;
	int pivot = begin;
	int key = a[begin];
 
	while (begin < end)
	{
		//右边找小
		while (begin < end && a[end] >= key) //这里如果不写begin<end的话可能会出现越界访问
		{
			--end;
		}
		//小的放到左边的坑里，自己形成了新的坑位
		a[pivot] = a[end];
		pivot = end;
        
        //左边找大
		while (begin < end && a[begin] <= key)
		{
			++begin;
		}
		//大的放到左边的坑里，自己形成了新的坑位
		a[pivot] = a[begin];
		pivot = begin;
	}
 
	//当begin和end相遇，证明他们两都到了坑的位置
	pivot = begin;//随便给一个
	a[pivot] = key;
 
	//[left, pivot - 1] pivot [pivot+ 1, right]
	//左子区间和右子区间有序，我们就有序了，如何让他们有序呢？分治递归
	QuickSort(a, left, key - 1);
	QuickSort(a, key + 1, right);
}
 
//函数传参：QuickSort(arr, 0, sizeof(arr) / sizeof(int) - 1);

void QuickSort(int* a, int left, int right)//升序
{
	if (left >= right)
	{
		return;
	}
 
	int begin = left;
	int end = right;
	int keyi = begin;
 
	while (begin < end)
	{
		//找小
		while (begin < end && a[end] >= a[keyi])
		{
			--end;
		}
		//找大
		while (begin < end && a[begin] <= a[keyi])
		{
			++begin;
		}
		Swap(&a[begin], &a[end]);
	}
 
	Swap(&a[begin], &a[keyi]);
	keyi = begin;
 
	//[left, keyi - 1] keyIndex [keyi + 1, right]
	//左子区间和右子区间有序，我们就有序了，如何让他们有序呢？分治递归
 
	QuickSort(a, left, keyi - 1);
	QuickSort(a, keyi + 1, right);
}

void QuickSort(int* a, int left, int right)//升序
{
	if (left >= right)
	{
		return;
	}
 
	int keyi = left;
	int prev = left;
	int cur = left + 1;
	while (cur <= right)
	{
        //++prev != cur为了防止自己跟自己交换造成不必要的消耗
		if (a[cur] < a[keyi] && ++prev != cur)
		{
			Swap(&a[prev], &a[cur]);
		}
		++cur;
	}
	Swap(&a[keyi], &a[prev]);
	keyi = prev;
	
	//[left, keyi - 1] keyi [keyi + 1, right]
	//左子区间和右子区间有序，我们就有序了，如何让他们有序呢？分治递归
 
	QuickSort(a, left, keyi - 1);
	QuickSort(a, keyi + 1, right);
}

void _MergeSort(int* a, int left, int right, int* tmp)
{
	if (left >= right)
		return;
 
	int mid = (left + right) >> 1;
	// 假设[left, mid] [mid + 1, right] 有序，那么我们就可以归并了
	_MergeSort(a, left, mid, tmp);
	_MergeSort(a, mid + 1, right, tmp);
 
	//归并
	int begin1 = left, end1 = mid;
	int begin2 = mid + 1, end2 = right;
	int index = left;
	while (begin1 <= end1 && begin2 <= end2)
	{
		if (a[begin1] < a[begin2])
		{
			tmp[index++] = a[begin1++];
		}
		else
		{
			tmp[index++] = a[begin2++];
		}
	}
 
	while (begin1 <= end1)
	{
		tmp[index++] = a[begin1++];
	}
 
	while (begin2 <= end2)
	{
		tmp[index++] = a[begin2++];
	}
 
	//拷贝回去
	for (int i = left; i <= right; ++i)
	{
		a[i] = tmp[i];
	}
}
 
void MergeSort(int* a, int n)
{
	int* tmp = (int*)malloc(sizeof(int) * n);
	_MergeSort(a, 0, n - 1, tmp);
 
	free(tmp);
}