问题
Can this be cleaned up?
using System;
class AscendingBubbleSort
{
public static void Main()
{
int i = 0,j = 0,t = 0;
int []c=new int[20];
for(i=0;i<20;i++)
{
Console.WriteLine("Enter Value p[{0}]:", i);
c[i]=int.Parse(Console.ReadLine());
}
// Sorting: Bubble Sort
for(i=0;i<20;i++)
{
for(j=i+1;j<20;j++)
{
if(c[i]>c[j])
{
Console.WriteLine("c[{0}]={1}, c[{2}]={3}", i, c[i], j, c[j]);
t=c[i];
c[i]=c[j];
c[j]=t;
}
}
}
Console.WriteLine("bubble sorted array:");
// sorted array output
for(i=0;i<20;i++)
{
Console.WriteLine ("c[{0}]={1}", i, c[i]);
}
}
}
回答1:
What you've pasted there isn't a bubble sort. It's a sort of "brute force" sort but it's not bubble sort. Here's an example of a generic bubble sort. It uses an arbitrary comparer, but lets you omit it in which case the default comparer is used for the relevant type. It will sort any (non-readonly) implementation of IList<T>, which includes arrays. Read the above link (to Wikipedia) to get more of an idea of how bubble sort is meant to work. Note how on each loop we go through from start to finish, but only compare each item with its neighbour. It's still an O(n2) sort algorithm, but in many cases it will be quicker than the version you've given.
public void BubbleSort<T>(IList<T> list)
{
BubbleSort<T>(list, Comparer<T>.Default);
}
public void BubbleSort<T>(IList<T> list, IComparer<T> comparer)
{
bool stillGoing = true;
while (stillGoing)
{
stillGoing = false;
for (int i = 0; i < list.Count-1; i++)
{
T x = list[i];
T y = list[i + 1];
if (comparer.Compare(x, y) > 0)
{
list[i] = y;
list[i + 1] = x;
stillGoing = true;
}
}
}
}
回答2:
The most elegant way to sort in C# is
Array.Sort( object[] )
That will work everywhere except in homework problems where the teacher asked you to implement the non-elegant bubble sort algorithm. ;-)
回答3:
Overall, there's nothing wrong with your bubble sort implementation. If I were doing a real code review, I'd make the following changes:
Choose more descriptive variable names
Why is your array just called c?
Minimize variable scope
All of your variables are declared at the top of the function. Unless this is a homework requirement or a coding standard, its more idiomatic to declare variables "close" to the location where they are used, preferably so they have the smallest amount of scope possible.
So, eliminate the first line which reads int i = 0,j = 0,t = 0;. Declare loop counters inline:
for(int i = 0; i < 20; i++)
And declare your temp variable in the place where its used:
Console.WriteLine("c[{0}]={1}, c[{2}]={3}", i, c[i], j, c[j]);
int t=c[i];
c[i]=c[j];
c[j]=t;
Eliminate hard-coded array bounds.
This:
for(i=0;i<20;i++)
Becomes this:
for(i = 0; i < c.Length; i++)
回答4:
Most people would not bother making a bubble sort elegant. In general, though, I find that doing this:
for (int i = 0; i < items.Length; i++) {
Item item = items[i];
// do something with item
}
is both more elegant and more maintainable than doing this:
Item item;
int i;
for (i = 0; i < items.Length; i++) {
item = items[i];
// do something with item
}
In other words, declare your variables within the smallest applicable scope. Otherwise you might find yourself doing something with i or item at some other point in the code and then using them again where you shouldn't be.
回答5:
I would use a swap methed to swap the two array items. (details of how to write swap method left as homework!)
You should think about the case when the items are already in order
You should read up on Insertion sort for more marks :-)
Rather then reading the test data from the keyboard, see if you can learn how to use nUnit
回答6:
I personally prefer this:
string foo [] = new string[] {"abc", "def", "aaa", "feaf", "afea" };
Array.Sort(foo);
But that's just me. Sort is a solved problem, why reinvent the wheel?
回答7:
I believe there is an improvement in the answer proposed by Jon Skeet. After each loop, the number of iterations should exclude the last item processed in the previous iteration. So, here's the code:
public void BubbleSortImproved<T>(IList<T> list)
{
BubbleSortImproved<T>(list, Comparer<T>.Default);
}
public void BubbleSortImproved<T>(IList<T> list, IComparer<T> comparer)
{
bool stillGoing = true;
int k = 0;
while (stillGoing)
{
stillGoing = false;
//reduce the iterations number after each loop
for (int i = 0; i < list.Count - 1 - k; i++)
{
T x = list[i];
T y = list[i + 1];
if (comparer.Compare(x, y) > 0)
{
list[i] = y;
list[i + 1] = x;
stillGoing = true;
}
}
k++;
}
}
回答8:
int[] array = {4,5,7,1,8};
int n1, n2;
bool stillgoing = true;
while (stillgoing)
{
stillgoing = false;
for (int i = 0; i < (array.Length-1); i++)
{
if (array[i] > array[i + 1])
{
n1 = array[i + 1];
n2 = array[i];
array[i] = n1;
array[i + 1] = n2;
stillgoing = true;
}
}
}
for (int i = 0; i < array.Length; i++)
{
Console.WriteLine(array[i]);
}
Took some ideas from Jon skeet...
回答9:
public int[] BubbleSortInAesc(int[] input)
{
for (int i = input.Length; i > 0; i--)
{
for (int j = 0; j < i-1; j++)
{
if (input[j] > input[j + 1])
{
//Swap the numbers
input[j] = input[j + 1]+input[j];
input[j + 1] = input[j] - input[j + 1];
input[j] = input[j] - input[j + 1];
}
}
}
return input;
}
回答10:
I think your algorithm in ok, but I would put the sort functionality in a seperate class and method.
来源：https://stackoverflow.com/questions/1595244/whats-the-most-elegant-way-to-bubble-sort-in-c