七大经典排序算法图解

void InsertSort(int* a, int n)
{
	for (int i = 0; i < n - 1; i++)
	{
		int end = i;
		int x = a[end + 1];
		while (end >= 0)
		{
			if (a[end] > x)
			{
				a[end + 1] = a[end];
				end--;
			}
			else
				break;
		}
		a[end + 1] = x;
	}
}

void ShellSort(int* a, int n)
{
	//多次预排序(gap > 1) + 直接插入( gap == 1)
	int gap = n;
	while (gap > 1)
	{
		//使gap最后一次一定能到1
		gap = gap / 3 + 1;
		//多组一起排
		for (int i = 0; i < n - gap; ++i)
		{
			int end = i;
			int x = a[end + gap];
			while (end >= 0)
			{
				if (a[end] > x)
				{
					a[end + gap] = a[end];
					end -= gap;
				}
				else
					break;
			}
			a[end + gap] = x;
		}
	}
}

void Swap(int* px, int* py)
{
	int tmp = *px;
	*px = *py;
	*py = tmp;
}
 
void SelectSort(int* a, int n)
{
	int begin = 0;
	while (begin < n - 1)
	{
		int mini = begin;
		for (int i = begin; i < n; i++)
		{
			if (a[i] < a[mini])
				mini = i;
		}
		Swap(&a[begin], &a[mini]);
		++begin;
	}
}

void Swap(int* px, int* py)
{
	int tmp = *px;
	*px = *py;
	*py = tmp;
}
 
//建大堆的向下调整算法
void AdjustDown(int* a, int n, int parent)
{
	int child = parent * 2 + 1;
	while (child < n)
	{
		if (child + 1 < n && a[child + 1] > a[child])
			++child;
		if (a[child] > a[parent])
		{
			Swap(&a[child], &a[parent]);
			parent = child;
			child = parent * 2 + 1;
		}
		else
			break;
	}
}
 
void HeapSort(int* a, int n)
{
    //先使用向下调整算法，从最后一个元素的父亲开始建堆
	for (int i = (n - 1 - 1) / 2; i >= 0; --i)
	{
		AdjustDown(a, n, i);
	}
    //先交换，再调整
	for (int end = n - 1; end > 0; --end)
	{
		Swap(&a[0], &a[end]);
		AdjustDown(a, end, 0);
	}
}

void Swap(int* px, int* py)
{
	int tmp = *px;
	*px = *py;
	*py = tmp;
}
 
void BubbleSort(int* a, int n)
{
	for (int j = 0; j < n; j++)
	{
		for (int i = 0; i < n - j - 1; i++)
		{
			if (a[i] > a[i + 1])
			{
				Swap(&a[i], &a[i + 1]);
			}
		}
	}
}

void QuickSort(int* a, int left, int right)
{
	if (left >= right)
		return;
 
    //先将选定的基准值排好
	int keyi = Partion(a, left, right);
 
    //再通过递归排序其左右子序列
	QuickSort(a, left, keyi - 1);
	QuickSort(a, keyi + 1, right);
}

//hoare版本
int Partion(int* a, int left, int right)
{
	int keyi = left;
	while (left < right)
	{
		//右边先走，找小
		while (left < right && a[right] >= a[keyi])
		{
			--right;
		}
		//左边走，找大
		while (left < right && a[left] <= a[keyi])
		{
			++left;
		}
		Swap(&a[left], &a[right]);
	}
	Swap(&a[keyi], &a[left]);
	return left;
}

//挖坑法
int Partion(int* a, int left, int right)
{
    int key = a[left];
	int pivot = left;
	while (left < right)
	{
		//右边先走，找小
		while (left < right && a[right] >= key)
		{
			--right;
		}
		//值覆盖，坑替换
		a[pivot] = a[right];
		pivot = right;
		//左边走，找大
		while (left < right && a[left] <= key)
		{
			++left;
		}
		//值覆盖，坑替换
		a[pivot] = a[left];
		pivot = left;
	}
	a[pivot] = key;
	return pivot;
}

//前后指针法 ——更推荐
int Partion(int* a, int left, int right)
{
	int keyi = left;
	int cur = left + 1;
	int prev = left;
	while (cur <= right)
	{
		//cur找小，把小的换到左边
		if (a[cur] < a[keyi])
		{
            ++prev;
			Swap(&a[cur], &a[prev]);
		}
		++cur;
	}
	Swap(&a[prev], &a[keyi]);
	return prev;
}

//三数取中
int GetMidIndex(int* a, int left, int right)
{
	int mid = (left + right) / 2;
	if (a[left] > a[mid])
	{
		if (a[mid] > a[right])
			return mid;
		else if (a[left] < a[right])
			return left;
		else
			return right;
	}
	else
	{
		if (a[mid] < a[right])
			return mid;
		else if (a[left] > a[right])
			return left;
		else
			return right;
	}
}

//三数取中
int GetMidIndex(int* a, int left, int right)
{
	//int mid = (left + right) / 2;
	int mid = left + ((right - left) >> 1);
	if (a[left] > a[mid])
	{
		if (a[mid] > a[right])
			return mid;
		else if (a[left] < a[right])
			return left;
		else
			return right;
	}
	else
	{
		if (a[mid] < a[right])
			return mid;
		else if (a[left] > a[right])
			return left;
		else
			return right;
	}
}
 
void Swap(int* px, int* py)
{
	int tmp = *px;
	*px = *py;
	*py = tmp;
}
 
//前后指针法
int Partion(int* a, int left, int right)
{
	int midi = GetMidIndex(a, left, right);
	Swap(&a[midi], &a[left]);
 
	int keyi = left;
	int cur = left + 1;
	int prev = left;
	while (cur <= right)
	{
		//cur找小，把小的换到左边
		if (a[cur] < a[keyi] && ++prev != cur)
		{
			Swap(&a[cur], &a[prev]);
		}
		++cur;
	}
	Swap(&a[prev], &a[keyi]);
	return prev;
}
 
void QuickSort(int* a, int left, int right)
{
	if (left >= right)
		return;
 
	int keyi = Partion3(a, left, right);
 
	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 - left) >> 1);
	_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 i = left;
	while (begin1 <= end1 && begin2 <= end2)
	{
		if (a[begin1] <= a[begin2])
		{
			tmp[i++] = a[begin1++];
		}
		else
		{
			tmp[i++] = a[begin2++];
		}
	}
	while (begin1 <= end1)
	{
		tmp[i++] = a[begin1++];
	}
	while (begin2 <= end2)
	{
		tmp[i++] = a[begin2++];
	}
 
	//把排序后的元素拷贝回原来的数组
	for (int j = left; j <= right; ++j)
	{
		a[j] = tmp[j];
	}
}
 
void MergeSort(int* a, int n)
{
	int* tmp = (int*)malloc(sizeof(int) * n);
	if (tmp == NULL)
	{
		printf("malloc fail\n");
		exit(-1);
	}
 
	_MergeSort(a, 0, n - 1, tmp);
 
	free(tmp);
	tmp = NULL;
}