问题
Currently my Quick Sort algorithm sorts the array in Ascending order in case 1 but I would like to make it so that when the user selects option 2 (case 2) then it sorts the array in Descending order. Do I have to create 2 separate algorithms for each case? Or is there a simpler and more efficient way?
Appreciate the help.
static void Main(string[] args)
{
Console.WriteLine("Analysis of Seismic Data.\n");
Console.WriteLine("Selection of Arrays:");
//Display all the options.
Console.WriteLine("1-Year");
Console.WriteLine("2-Month");
Console.WriteLine("3-Day");
Console.WriteLine("4-Time");
Console.WriteLine("5-Magnitude");
Console.WriteLine("6-Latitude");
Console.WriteLine("7-Longitude");
Console.WriteLine("8-Depth");
Console.WriteLine("9-Region");
Console.WriteLine("10-IRIS_ID");
Console.WriteLine("11-Timestamp\n\n");
Console.WriteLine("Use numbers to select options.");
//Read in user's decision.
Console.Write("Select which array is to be analysed:");
int userDecision = Convert.ToInt32(Console.ReadLine());
//Selected which array is to be analyzed
switch (userDecision)
{
case 1:
Console.WriteLine("\nWould you like to sort the Array in Ascending or Descending order?");
Console.WriteLine("1-Ascending");
Console.WriteLine("2-Descending");
//Create another switch statement to select either ascending or descending sort.
int userDecision2 = Convert.ToInt32(Console.ReadLine());
switch (userDecision2)
{
case 1:
//Here algorithm sorts my array in ascending order by default.
QuickSort(Years);
Console.WriteLine("Contents of the Ascending Year array: ");
foreach (var year in Years)
{
Console.WriteLine(year);
}
break;
case 2:
//How do I sort the same array in Descending order when Option 2 is selected?
//QuickSort(Years) Descendingly.
Console.WriteLine("Contents of the Descending Year array: ");
foreach (var year in Years)
{
Console.WriteLine(year);
}
break;
}
break;
case 2:
Console.WriteLine("\nWould you like to sort the Array in Ascending or Descending order?");
Console.WriteLine("1-Ascending");
Console.WriteLine("2-Descending");
//Create another switch statement to select either ascending or descending sort.
int userDecision3 = Convert.ToInt32(Console.ReadLine());
switch (userDecision3)
{
case 1:
QuickSort(Years);
Console.WriteLine("Contents of the Ascending Month array: ");
foreach (var month in Months)
{
Console.WriteLine(month);
}
break;
case 2:
//Same problem, how do I sort it in descending order?
Console.WriteLine("Contents of the Descending month array: ");
foreach (var month in Months)
{
Console.WriteLine();
}
break;
}
break;
}
}
public static void QuickSort<T>(T[] data) where T : IComparable<T>
{
Quick_Sort(data, 0, data.Length - 1);
}
public static void Quick_Sort<T>(T[] data, int left, int right) where T : IComparable<T>
{
int i, j;
T pivot, temp;
i = left;
j = right;
pivot = data[(left + right) / 2];
do
{
while ((data[i].CompareTo(pivot) < 0) && (i < right)) i++;
while ((pivot.CompareTo(data[j]) < 0) && (j > left)) j--;
if (i <= j)
{
temp = data[i];
data[i] = data[j];
data[j] = temp;
i++;
j--;
}
} while (i <= j);
if (left < j) Quick_Sort(data, left, j);
if (i < right) Quick_Sort(data, i, right);
}
回答1:
You can change your Quicksort method to accept an IComparer<T> comparer, and then use that to make the comparisons.
Then you can use Comparer<T>.Default if you want the default comparison order, or you can use Comparer<T>.Create() to create a custom (e.g. reversed) comparison.
Compilable example:
using System;
using System.Collections.Generic;
namespace ConsoleApp1
{
class Program
{
static void Main()
{
int[] data = {6, 7, 2, 3, 8, 1, 9, 0, 5, 4};
QuickSort(data);
Console.WriteLine(string.Join(", ", data)); // Prints 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
QuickSort(data, Comparer<int>.Create((a, b) => b.CompareTo(a)));
Console.WriteLine(string.Join(", ", data)); // Prints 9, 8, 7, 6, 5, 4, 3, 2, 1, 0
}
public static void QuickSort<T>(T[] data)
{
Quick_Sort(data, 0, data.Length - 1, Comparer<T>.Default);
}
public static void QuickSort<T>(T[] data, IComparer<T> comparer)
{
Quick_Sort(data, 0, data.Length - 1, comparer);
}
public static void Quick_Sort<T>(T[] data, int left, int right, IComparer<T> comparer)
{
int i, j;
T pivot, temp;
i = left;
j = right;
pivot = data[(left + right) / 2];
do
{
while ( (comparer.Compare(data[i], pivot) < 0) && (i < right)) i++;
while ( (comparer.Compare(pivot, data[j]) < 0) && (j > left)) j--;
if (i <= j)
{
temp = data[i];
data[i] = data[j];
data[j] = temp;
i++;
j--;
}
} while (i <= j);
if (left < j) Quick_Sort(data, left, j, comparer);
if (i < right) Quick_Sort(data, i, right, comparer);
}
}
}
This has two advantages:
- The type
Tdoes NOT need to implementIComparable<T>. You can pass in anIComparer<T>object that does the comparison. - You can sort the same data in multiple ways, by passing in different custom
IComparer<T>object.
This is the approach adopted by a number of the Linq IEnumerable extensions, for example Enumerable.OrderBy()
回答2:
Add parameter that allows to change result of comparisons
(data[i].CompareTo(pivot) < 0)
and
(pivot.CompareTo(data[j]) < 0)
One simple way: argument descending +1/-1 and use
data[i].CompareTo(pivot) * descending < 0
回答3:
Just adding a bit of cream on @Matthew Watson answer. As after reading the post from @Illimar he wanted to give the user the choice in sorting the Array either in Ascending mode or in Descending mode. I have just edited @Matthew work to come up with the following:
using System;
using System.Collections.Generic;
using System.Threading;
namespace Test1
{
class Program
{
static void Main(string[] args)
{
MySorter();
}
static void MySorter()
{
int[] data = MyArray();
Console.WriteLine();
Console.WriteLine("Chose 1 to sort Ascending or 2 to sort Descending:");
//int choice = Console.Read();
ConsoleKeyInfo choice = Console.ReadKey();
Console.WriteLine();
if (choice.Key == ConsoleKey.D1 || choice.Key == ConsoleKey.NumPad1)
{
QuickSort(data);
string result = string.Join(", ", data);
Console.WriteLine(result);
Thread.Sleep(4000);
}
else if (choice.Key == ConsoleKey.D2 || choice.Key == ConsoleKey.NumPad2)
{
QuickSort(data, Comparer<int>.Create((a, b) => b.CompareTo(a)));
Console.WriteLine(string.Join(", ", data));
Thread.Sleep(4000);
}
else
{
Console.WriteLine("wrong input.");
Thread.Sleep(2000);
Environment.Exit(0);
}
}
public static int[] MyArray()
{
Console.WriteLine("Enter a total of 10 numbers to be sorted: ");
int[] InputData = new int[10];
for (int i = 0; i < InputData.Length; i++)
{
var pressedkey = Console.ReadKey();
int number;
bool result = int.TryParse(pressedkey.KeyChar.ToString(), out number);
if (result)
{
InputData[i] = number;
}
}
return InputData;
}
public static void QuickSort<T>(T[] data)
{
Quick_Sort(data, 0, data.Length - 1, Comparer<T>.Default);
}
public static void QuickSort<T>(T[] data, IComparer<T> comparer)
{
Quick_Sort(data, 0, data.Length - 1, comparer);
}
public static void Quick_Sort<T>(T[] data, int left, int right, IComparer<T> comparer)
{
int i, j;
T pivot, temp;
i = left;
j = right;
pivot = data[(left + right) / 2];
do
{
while ((comparer.Compare(data[i], pivot) < 0) && (i < right)) i++;
while ((comparer.Compare(pivot, data[j]) < 0) && (j > left)) j--;
if (i <= j)
{
temp = data[i];
data[i] = data[j];
data[j] = temp;
i++;
j--;
}
} while (i <= j);
if (left < j) Quick_Sort(data, left, j, comparer);
if (i < right) Quick_Sort(data, i, right, comparer);
}
}
}
So In the above the User gives the numbers to be sorted as Input and then chooses how the sorting should be done?
来源：https://stackoverflow.com/questions/43803531/how-can-i-make-my-quick-sort-algorithm-sort-the-arrays-in-both-ascending-and-des