常用排序算法总结

/******************************************
不稳定的排序算法：
选择排序（selection sort）— O(n^2)
希尔排序（shell sort）— O(nlog n) 如果使用最佳的现在版本
堆排序（heapsort）— O(nlog n)
快速排序（quicksort）— O(nlog n) 期望时间，O(n^2) 最坏情况； 对于大的、乱数列表一般相信是最快的已知排序
*******************************************/

//插入排序
void InsertionSort( int *arr, int length )
{
	if ( arr == NULL || length < 2 )    
		return;
	for( int index = 1; index < length; ++index )
	{
		int key = arr[index];
		int j = index - 1;

		for( ; j >= 0 && key < arr[j]; --j )
			arr[ j+1 ] = arr[j];

		arr[j+1] = key;
	}
}

//冒泡排序
void BubbleSort( int *arr, int length )
{
	if ( arr == NULL || length < 2 )
		return;

	bool IsChanged = true;

	for ( int i = 0; i < length; ++i )
	{
		if ( IsChanged == false ) return;

		for ( int j = length - 1; j > i; --j )
		{
			IsChanged = false;
			if ( arr[j] < arr[j-1] )
			{
				swap( arr[j], arr[j-1] );
				IsChanged = true;
			}
		}
	}

}




//维基百科的方法，划分“增量”以后，不是对每一个子数组进行插入排序，
//而是对整个数组进行扫描，进行整个的插入排序
//希尔排序
void ShellSort(int *data, size_t size)
{
	for (int gap = size / 2; gap > 0; gap /= 2)
		for ( int i = gap; i < size; ++i )
		{
			int key = data[i];
			int j = 0;
			for( j = i -gap; j >= 0 && data[j] > key; j = j - gap )
			{
				data[j+gap] = data[j];
			}  
			data[j+gap] = key;
		}
}

void Merge( int arr[], int nBegin, int nMid, int nEnd )
{
	int lengthL = nMid - nBegin + 1;
	int lengthR = nEnd -nMid;

	int *L = new int [ lengthL +1 ];
	int *R = new int [ lengthR + 1 ];

	for( int i = 0; i < lengthL; ++i )
		L[i] = arr[ nBegin + i ];

	for( int i = 0; i < lengthR; ++i )
		R[i] = arr[ nMid + i + 1 ];

	L[ lengthL ] = INT_MAX;
	R[ lengthR ] = INT_MAX;

	int indexL = 0;
	int indexR = 0;

	for ( int i = nBegin; i <= nEnd; ++i )
	{
		if ( L[ indexL ] <= R[ indexR ] )
		{
			arr[ i ] = L[ indexL ];
			++indexL;
		}
		else {
			arr[ i ] = R[ indexR ];
			++indexR;
		}

	}

	delete [] L;
	delete [] R;
}

//归并排序
void MergeSort( int arr[], int start, int end )
{
	if ( end > start )
	{
		int mid = (end + start) / 2;
		MergeSort( arr, start, mid);
		MergeSort( arr, mid + 1,end );
		Merge( arr,start, mid,end );
	}
}



int  Partition ( int data[], int start, int end )
{
     int index = data[end];
	 int i = start - 1;
	 for ( int j = start ; j < end ; ++j )
	 {
		 if ( data[j] <= index )
		 {
			 ++i;
			 swap( data[i], data[j] );
		 }
	 }
	 swap( data[i+1], data[end] );
	 return i+1;
}

//快速排序
void  QuickSort( int data[], int start, int end )
{
	if ( start < end )
	{
		int mid = Partition ( data, start,end );
        QuickSort( data, start, mid -1 );
		QuickSort( data, mid + 1, end );
	}
}