冒泡排序与选择排序的不同、快速排序与选择排序的结合
2013-05-10 00:11
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冒泡排序与选择排序的不同、快速排序与选择排序的结合
冒泡排序可以说是最简单的排序了。我们学习C语言循环的时候都会提到。
可见这是一种浅而易懂的排序算法!
但不见得这种算法就没用处。首先,他很容易理解,这样在各种教材中比较适合拿来“开门见山”。其次是他很稳定。 若明确知道即将排的数字很混乱,随机性很强,则用冒泡排序也未偿不可。 谁让他始终是O(n^2)呢。
冒泡排序法代码:
1
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
void BubbleSort(int a[],int l)
2
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
3
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(int i = 0; i< l;++i)
4
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
5
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(int j = i+1; j< l; ++j)
6
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
7
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
if(a[j]<a[i])
8
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
9
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int t = a[i];
10
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
a[i] = a[j];
11
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
a[j] = t;
12
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
13
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
14
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
15
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockEnd.gif)
}
从中我们可以看到,每次都会将后面的L-(i+1)个数拿来和a[i]比较,然后将小一点的换到前面。有人就觉得啊,这个每次都交换很费性能,影响效率。所以他们就将a[j]和a[i]比较后的最小值的下标记下来,当比较完之后,最后记下的下标就是最小的值的下标,然后再进行一次交换。于是便有了选择排序法。
选择排序法代码:
1
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
void SelectSort(int a[],int l)
2
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
3
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(int i = 0; i< l; ++i)
4
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
5
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int k=i;
6
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(int j = i+1; j<l;++j)
7
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
8
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
9
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
if(a[j]<a[k])
10
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
11
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
k=j;
12
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
13
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
14
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int t = a[i];
15
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
a[i]=a[k];
16
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
a[k]= t;
17
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
18
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockEnd.gif)
}
虽然,我们并没有根本性地扭转冒泡排序的地位。但效率是有明显提升的,至少减少了L*(L-1)-L = L*(L-2) = L^2 - 2*L次交换!
另外,目前广为使用的快速排序和选择排序联合使用,也会有意想不到的提升!
众所周知,当用快速排序法排序时,划分到很细的时候,明显很亏。 比如:两三个数排序却要划分成两堆,这样很划不来。所以,我们可以设定一个阀值,当快速排序划分到一定粒度的时候,便采用选择排序。 至于这个阀值,可以通过performace来测试,以得到一个“最优值”
1
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
void QSort(int a[],int l,int r)
2
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
3
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int p;
4
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
if(l<r)
5
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
6
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
if(l-r<= DEFINE_NUMBER)
7
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
SelectSort(a,l,r);
8
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
else
9
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
10
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
p = Partition(a,l,r);
11
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
QSort(a,l,p-1);
12
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
QSort(a,p+1,r);
13
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
14
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
15
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockEnd.gif)
}
冒泡排序可以说是最简单的排序了。我们学习C语言循环的时候都会提到。
可见这是一种浅而易懂的排序算法!
但不见得这种算法就没用处。首先,他很容易理解,这样在各种教材中比较适合拿来“开门见山”。其次是他很稳定。 若明确知道即将排的数字很混乱,随机性很强,则用冒泡排序也未偿不可。 谁让他始终是O(n^2)呢。
冒泡排序法代码:
1
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
void BubbleSort(int a[],int l)
2
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
3
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(int i = 0; i< l;++i)
4
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
5
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(int j = i+1; j< l; ++j)
6
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
7
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
if(a[j]<a[i])
8
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
9
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int t = a[i];
10
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
a[i] = a[j];
11
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
a[j] = t;
12
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
13
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
14
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
15
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockEnd.gif)
}
从中我们可以看到,每次都会将后面的L-(i+1)个数拿来和a[i]比较,然后将小一点的换到前面。有人就觉得啊,这个每次都交换很费性能,影响效率。所以他们就将a[j]和a[i]比较后的最小值的下标记下来,当比较完之后,最后记下的下标就是最小的值的下标,然后再进行一次交换。于是便有了选择排序法。
选择排序法代码:
1
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
void SelectSort(int a[],int l)
2
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
3
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(int i = 0; i< l; ++i)
4
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
5
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int k=i;
6
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
for(int j = i+1; j<l;++j)
7
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
8
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
9
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
if(a[j]<a[k])
10
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
11
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
k=j;
12
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
13
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
14
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int t = a[i];
15
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
a[i]=a[k];
16
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
a[k]= t;
17
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
18
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockEnd.gif)
}
虽然,我们并没有根本性地扭转冒泡排序的地位。但效率是有明显提升的,至少减少了L*(L-1)-L = L*(L-2) = L^2 - 2*L次交换!
另外,目前广为使用的快速排序和选择排序联合使用,也会有意想不到的提升!
众所周知,当用快速排序法排序时,划分到很细的时候,明显很亏。 比如:两三个数排序却要划分成两堆,这样很划不来。所以,我们可以设定一个阀值,当快速排序划分到一定粒度的时候,便采用选择排序。 至于这个阀值,可以通过performace来测试,以得到一个“最优值”
1
![](http://www.cppblog.com/Images/OutliningIndicators/None.gif)
void QSort(int a[],int l,int r)
2
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
3
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
int p;
4
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
if(l<r)
5
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
6
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
if(l-r<= DEFINE_NUMBER)
7
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
SelectSort(a,l,r);
8
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
else
9
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://www.cppblog.com/Images/OutliningIndicators/ContractedSubBlock.gif)
![](http://www.cppblog.com/Images/dot.gif)
{
10
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
p = Partition(a,l,r);
11
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
QSort(a,l,p-1);
12
![](http://www.cppblog.com/Images/OutliningIndicators/InBlock.gif)
QSort(a,p+1,r);
13
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
14
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedSubBlockEnd.gif)
}
15
![](http://www.cppblog.com/Images/OutliningIndicators/ExpandedBlockEnd.gif)
}
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