[C#/COMMON] 조합 구하기

▶ 조합 구하기 예제

using System;

long combination = GetCombination(3, 2);

Console.WriteLine(combination);

 

728x90

 

▶ 조합 구하기

#region 조합 구하기 - GetCombination(totalCount, extractionCount)

/// <summary>
/// 조합 구하기
/// </summary>
/// <param name="totalCount">전체 수</param>
/// <param name="extractionCount">추출 수</param>
/// <returns>조합</returns>
public long GetCombination(int totalCount, int extractionCount)
{
    return GetPermutation(totalCount, extractionCount) / GetFactorial(extractionCount);
}

#endregion

#region 팩토리얼 분할 구하기 - GetFactorialDivision(topFactorial, divisorFactorial)

/// <summary>
/// 팩토리얼 분할 구하기
/// </summary>
/// <param name="topFactorial">상위 팩토리얼</param>
/// <param name="divisorFactorial">제수 팩토리얼</param>
/// <returns>팩토리얼 분할</returns>
private long GetFactorialDivision(int topFactorial, int divisorFactorial)
{
    long result = 1;

    for(int i = topFactorial; i > divisorFactorial; i--)
    {
        result *= i;
    }

    return result;
}

#endregion
#region 순열 구하기 - GetPermutation(totalCount, extractionCount)

/// <summary>
/// 순열 구하기
/// </summary>
/// <param name="totalCount">전체 수</param>
/// <param name="extractionCount">추출 수</param>
/// <returns>순열</returns>
private long GetPermutation(int totalCount, int extractionCount)
{
    return GetFactorialDivision(totalCount, totalCount - extractionCount);
}

#endregion
#region 팩토리얼 구하기 - GetFactorial(int i)

/// <summary>
/// 팩토리얼 구하기
/// </summary>
/// <param name="value">값</param>
/// <returns>팩토리얼</returns>
private long GetFactorial(int value)
{
    if(value <= 1)
    {
        return 1;
    }

    return value * GetFactorial(value - 1);
}

#endregion