为什么插入排序总是跳动在此实现归并排序? [英] Why is insertion sort always beating merge sort in this implementation?
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问题描述
我不明白:为什么我插入排序实施殴打,每次归并排序,任何规模的 N
公开名单<的Int32> InsertionSort(名单<的Int32>元素,布尔升=真)
{
对于(的Int32 J = 1; J< elements.Count; J ++)
{
INT32键=因素[J]。
INT32 I =的J - 1;
而(ⅰ> = 0&安培;及(元素[I] .CompareTo(键)大于0)==升序)
元素[I + 1] =元素[我 - ]。
元素[I + 1] =键;
}
返回元素;
}
公开名单<的Int32>归并(名单<的Int32>元素,布尔升=真)
{
排序(元素,0,elements.Count - 1);
返回元素;
}
私人无效归并(名单<的Int32>元素的Int32在startIndex,的Int32计数)
{
如果(在startIndex<计数)
{
INT32一半=(在startIndex +计数).Divide(2 RoundMethod.Floor);
排序(元素,在startIndex一半);
排序(元素,半数+ 1,计数);
合并(元素,在startIndex,一半,算);
}
}
公开名单<的Int32>合并(名单<的Int32>元素的Int32下界,的Int32一半的Int32上界)
{
的Int32 I = 0;
的Int32 J = 0;
INT32 lowerElementsCount =半 - 下界+ 1;
INT32 upperElementsCount =上界 - 半;
名单<的Int32>左=新的名单,其中,的Int32>();
而(I< lowerElementsCount)
left.Add(元素[下界+ I +]);
名单<的Int32>右=新的名单,其中,的Int32>();
而(J< upperElementsCount)
right.Add(元素[半数+ J + + + 1]);
left.Add(Int32.MaxValue);
right.Add(Int32.MaxValue);
I = 0;
J = 0;
对于(INT K =下界; K< =上界; k ++)
如果(左[1] - =右[J]。)
{
元素[K] =左[I]
我++;
}
其他
{
元素[K] =右[J]。
J ++;
}
返回元素;
}
下面是我的结果:
分拣1个元素
合并排序:花费时间:0毫秒(1513蜱)
插入排序:花费时间:0毫秒(1247蜱)
分拣10种元素
合并排序:花费时间:1毫秒(2710蜱)
插入排序:花费时间:0毫秒(3蜱)
分拣100个元素
合并排序:花费时间:0毫秒(273蜱)
插入排序:花费时间:0毫秒(11刻度)
分拣1000个元素
合并排序:花费时间:1毫秒(3142蜱)
插入排序:花费时间:0毫秒(72刻度)
分拣10000元素
合并排序:执行时间:18毫秒(30491蜱)
插入排序:花费时间:0毫秒(882蜱)
而code来进行测试:
静态无效的主要(字串[] args)
{
的for(int i = 1; I< 100000; I * = 10)
{
名单<的Int32>元素= GetFilledList(I,0,Int32.MaxValue,假);
Console.WriteLine(排序{0}元素,elements.Count);
秒表SW =新的秒表();
//合并排序
sw.Start();
新归并()排序(元素)。
sw.Stop();
Console.WriteLine(合并排序:花费时间:{0}毫秒({1}蜱),sw.ElapsedMilliseconds,sw.ElapsedTicks);
//插入排序
sw.Restart();
新InsertionSort()排序(元素)。
sw.Stop();
Console.WriteLine(插入分页:花费时间:{0}毫秒({1}蜱),sw.ElapsedMilliseconds,sw.ElapsedTicks);
Console.WriteLine();
}
Console.ReadKey();
}
在万一有人想知道我是从算法导论这些算法,托马斯H Cormen(作者)查尔斯E. Leiserson(作者),罗纳德·L.维斯特(作者),克利福德·斯坦(作者)
编辑:
静态列表<的Int32> GetFilledList(的Int32量的Int32下界,的Int32上界,布尔mayRepeat =真)
{
名单<的Int32>数=新的名单,其中,的Int32>();
随机R =新的随机();
的for(int i = 0; I<数量;我++)
{
INT32 NUMERO = r.Next(下界,上界);
而(mayRepeat&安培;!&安培; numbers.Contains(NUMERO))
NUMERO = r.Next(下界,上界);
numbers.Add(NUMERO);
}
返回的数字;
}
解决方案
因为,合并排序后,在元素中的对象已经排序。做的是另
元素= GetFilledList(I,0,Int32.MaxValue,假);
在
sw.Restart();
I don't understand: why is my insertion sort implementation beating merge sort every time, for any size of n
?
public List<Int32> InsertionSort(List<Int32> elements, Boolean ascending = true)
{
for (Int32 j = 1; j < elements.Count; j++)
{
Int32 key = elements[j];
Int32 i = j - 1;
while (i >= 0 && (elements[i].CompareTo(key) > 0) == ascending)
elements[i + 1] = elements[i--];
elements[i + 1] = key;
}
return elements;
}
public List<Int32> MergeSort(List<Int32> elements, Boolean ascending = true)
{
Sort(elements, 0, elements.Count - 1);
return elements;
}
private void MergeSort(List<Int32> elements, Int32 startIndex, Int32 count)
{
if(startIndex < count)
{
Int32 half = (startIndex + count).Divide(2, RoundMethod.Floor);
Sort(elements, startIndex, half);
Sort(elements, half + 1, count);
Merge(elements, startIndex, half, count);
}
}
public List<Int32> Merge(List<Int32> elements, Int32 lowerBound, Int32 half, Int32 upperBound)
{
Int32 i = 0;
Int32 j = 0;
Int32 lowerElementsCount = half - lowerBound + 1;
Int32 upperElementsCount = upperBound - half;
List<Int32> left = new List<Int32>();
while (i < lowerElementsCount)
left.Add(elements[lowerBound + i++]);
List<Int32> right = new List<Int32>();
while (j < upperElementsCount)
right.Add(elements[half + j++ + 1]);
left.Add(Int32.MaxValue);
right.Add(Int32.MaxValue);
i = 0;
j = 0;
for (int k = lowerBound; k <= upperBound; k++)
if (left[i] <= right[j])
{
elements[k] = left[i];
i++;
}
else
{
elements[k] = right[j];
j++;
}
return elements;
}
Here are my results:
SORTING 1 ELEMENTS
MERGE-SORT: TIME SPENT: 0ms (1513 ticks)
INSERTION-SORT: TIME SPENT: 0ms (1247 ticks)
SORTING 10 ELEMENTS
MERGE-SORT: TIME SPENT: 1ms (2710 ticks)
INSERTION-SORT: TIME SPENT: 0ms (3 ticks)
SORTING 100 ELEMENTS
MERGE-SORT: TIME SPENT: 0ms (273 ticks)
INSERTION-SORT: TIME SPENT: 0ms (11 ticks)
SORTING 1000 ELEMENTS
MERGE-SORT: TIME SPENT: 1ms (3142 ticks)
INSERTION-SORT: TIME SPENT: 0ms (72 ticks)
SORTING 10000 ELEMENTS
MERGE-SORT: TIME SPENT: 18ms (30491 ticks)
INSERTION-SORT: TIME SPENT: 0ms (882 ticks)
And the code for testing:
static void Main(string[] args)
{
for (int i = 1; i < 100000; i*=10)
{
List<Int32> elements = GetFilledList(i, 0, Int32.MaxValue, false);
Console.WriteLine("SORTING {0} ELEMENTS", elements.Count);
Stopwatch sw = new Stopwatch();
//MERGE SORT
sw.Start();
new MergeSort().Sort(elements);
sw.Stop();
Console.WriteLine("MERGE-SORT: TIME SPENT: {0}ms ({1} ticks)", sw.ElapsedMilliseconds, sw.ElapsedTicks);
//INSERTION SORT
sw.Restart();
new InsertionSort().Sort(elements);
sw.Stop();
Console.WriteLine("INSERTION-SORT: TIME SPENT: {0}ms ({1} ticks)", sw.ElapsedMilliseconds, sw.ElapsedTicks);
Console.WriteLine();
}
Console.ReadKey();
}
In case anyone wondering I got these algorithms from Introduction to Algorithms, Thomas H. Cormen (Author), Charles E. Leiserson (Author), Ronald L. Rivest (Author), Clifford Stein (Author)
EDIT:
static List<Int32> GetFilledList(Int32 quantity, Int32 lowerBound, Int32 upperBound, Boolean mayRepeat = true)
{
List<Int32> numbers = new List<Int32>();
Random r = new Random();
for (int i = 0; i < quantity; i++)
{
Int32 numero = r.Next(lowerBound, upperBound);
while(!mayRepeat && numbers.Contains(numero))
numero = r.Next(lowerBound, upperBound);
numbers.Add(numero);
}
return numbers;
}
解决方案
because, after the merge sort, the objects in elements are already sorted. do another
elements = GetFilledList(i, 0, Int32.MaxValue, false);
before the
sw.Restart();
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