Combinations and permutations: Difference between revisions
Add C# implementation
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}</syntaxhighlight>
=={{header|C#}}==
{{trans|Java}}
<syntaxhighlight lang="C#">
using System;
using System.Numerics;
class CombinationsAndPermutations
{
public static void Main(string[] args)
{
Console.WriteLine(double.MaxValue);
Console.WriteLine("A sample of permutations from 1 to 12 with exact Integer arithmetic:");
for (int n = 1; n <= 12; n++)
{
int k = n / 2;
Console.WriteLine($"{n} P {k} = {Permutation(n, k)}");
}
Console.WriteLine();
Console.WriteLine("A sample of combinations from 10 to 60 with exact Integer arithmetic:");
for (int n = 10; n <= 60; n += 5)
{
int k = n / 2;
Console.WriteLine($"{n} C {k} = {Combination(n, k)}");
}
Console.WriteLine();
Console.WriteLine("A sample of permutations from 5 to 15000 displayed in floating point arithmetic:");
Console.WriteLine($"{5} P {2} = {Display(Permutation(5, 2), 50)}");
for (int n = 1000; n <= 15000; n += 1000)
{
int k = n / 2;
Console.WriteLine($"{n} P {k} = {Display(Permutation(n, k), 50)}");
}
Console.WriteLine();
Console.WriteLine("A sample of combinations from 100 to 1000 displayed in floating point arithmetic:");
for (int n = 100; n <= 1000; n += 100)
{
int k = n / 2;
Console.WriteLine($"{n} C {k} = {Display(Combination(n, k), 50)}");
}
}
private static string Display(BigInteger val, int precision)
{
string s = val.ToString();
// Ensure that we don't try to take a substring longer than what's available.
int actualPrecision = Math.Min(precision, s.Length - 1); // Adjusted to ensure it doesn't exceed string length
System.Text.StringBuilder sb = new System.Text.StringBuilder();
if (s.Length > 1) // Check if the string has more than one character
{
sb.Append(s.Substring(0, 1));
sb.Append(".");
sb.Append(s.Substring(1, actualPrecision-1));
}
else
{
// If the string is only one digit, no need to insert a decimal point.
sb.Append(s);
}
sb.Append(" * 10^");
sb.Append(s.Length - 1);
return sb.ToString();
}
public static BigInteger Combination(int n, int k)
{
// Select value with smallest intermediate results
// combination(n, k) = combination(n, n-k)
if (n - k < k)
{
k = n - k;
}
BigInteger result = Permutation(n, k);
while (k > 0)
{
result = result / k;
k--;
}
return result;
}
public static BigInteger Permutation(int n, int k)
{
BigInteger result = BigInteger.One;
for (int i = n; i >= n - k + 1; i--)
{
result = result * i;
}
return result;
}
}
</syntaxhighlight>
{{out}}
<pre>
1.79769313486232E+308
A sample of permutations from 1 to 12 with exact Integer arithmetic:
1 P 0 = 1
2 P 1 = 2
3 P 1 = 3
4 P 2 = 12
5 P 2 = 20
6 P 3 = 120
7 P 3 = 210
8 P 4 = 1680
9 P 4 = 3024
10 P 5 = 30240
11 P 5 = 55440
12 P 6 = 665280
A sample of combinations from 10 to 60 with exact Integer arithmetic:
10 C 5 = 252
15 C 7 = 6435
20 C 10 = 184756
25 C 12 = 5200300
30 C 15 = 155117520
35 C 17 = 4537567650
40 C 20 = 137846528820
45 C 22 = 4116715363800
50 C 25 = 126410606437752
55 C 27 = 3824345300380220
60 C 30 = 118264581564861424
A sample of permutations from 5 to 15000 displayed in floating point arithmetic:
5 P 2 = 2. * 10^1
1000 P 500 = 3.2978863640988537122024252070116261706996485697981 * 10^1433
2000 P 1000 = 8.2415012140674255266380217928953202425839550211348 * 10^3167
3000 P 1500 = 8.6229457673788561572282325050469704818001698192368 * 10^5015
4000 P 2000 = 5.5146268042637929575202252487087217092097210095831 * 10^6937
5000 P 2500 = 2.5959899179479570425022364594725223975158226787173 * 10^8914
6000 P 3000 = 6.4684674799045492726351265543133876130483115297807 * 10^10934
7000 P 3500 = 3.6978393541988590953223392044469547113117500019066 * 10^12991
8000 P 4000 = 2.8347416494109128583587900207169062803923698647730 * 10^15079
9000 P 4500 = 3.5613559022062915735922606191272180393638776777367 * 10^17194
10000 P 5000 = 6.7310091721588924046678115055013992269082753633190 * 10^19333
11000 P 5500 = 7.1714299723894354619599359891785521535675525394493 * 10^21494
12000 P 6000 = 4.4778633072110971517945389774618813158941392935141 * 10^23675
13000 P 6500 = 3.6571405647713639990172807053439865891697112165983 * 10^25874
14000 P 7000 = 1.5680448683572888099973548116924953997328821172933 * 10^28090
15000 P 7500 = 2.2454775022523692436484435950526532351441855443096 * 10^30321
A sample of combinations from 100 to 1000 displayed in floating point arithmetic:
100 C 50 = 1.0089134454556419333481249725 * 10^29
200 C 100 = 9.0548514656103281165404177077484163874504589675413 * 10^58
300 C 150 = 9.3759702772827452793193754439064084879232655700081 * 10^88
400 C 200 = 1.0295250013541443297297588032040198675721092538107 * 10^119
500 C 250 = 1.1674431578827768292093473476217661965923008118031 * 10^149
600 C 300 = 1.3510794199619426851447487797850453039723394544919 * 10^179
700 C 350 = 1.5857433585316795487607022764754299250587342835720 * 10^209
800 C 400 = 1.8804244186835312700958607615195351332156581822914 * 10^239
900 C 450 = 2.2474718820660159573188913903771345843514101350359 * 10^269
1000 C 500 = 2.7028824094543656951561469362597527549615200844654 * 10^299
</pre>
=={{header|C++}}==
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