[C#/COMMON] 조합(Combination) 구하기

TestProject.zip

다운로드

▶ MainForm.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Windows.Forms;

namespace TestProject
{
    /// <summary>
    /// 메인 폼
    /// </summary>
    public partial class MainForm : Form
    {
        //////////////////////////////////////////////////////////////////////////////////////////////////// Constructor
        ////////////////////////////////////////////////////////////////////////////////////////// Public

        #region 생성자 - MainForm()

        /// <summary>
        /// 생성자
        /// </summary>
        public MainForm()
        {
            InitializeComponent();

            #region 이벤트를 설정한다.

            this.generateButton.Click += generateButton_Click;

            #endregion
        }

        #endregion

        //////////////////////////////////////////////////////////////////////////////////////////////////// Method
        ////////////////////////////////////////////////////////////////////////////////////////// Private
        //////////////////////////////////////////////////////////////////////////////// Event

        #region 생성 버튼 클릭시 처리하기 - generateButton_Click(sender, e)

        /// <summary>
        /// 생성 버튼 클릭시 처리하기
        /// </summary>
        /// <param name="sender">이벤트 발생자</param>
        /// <param name="e">이벤트 인자</param>
        private void generateButton_Click(object sender, EventArgs e)
        {
            string[] itemArray = txtItems.Text.Split(' ');

            int selectionCount = int.Parse(this.selectionCountTextBox.Text);

            List<List<string>> resultList = GetCombinationList<string>(itemArray.ToList(), selectionCount);

            this.combinationListBox.Items.Clear();

            foreach(List<string> result in resultList)
            {
                this.combinationListBox.Items.Add(string.Join(" ", result.ToArray()));
            }

            decimal combinationCount = GetCombinationCount(itemArray.Length, selectionCount);

            this.combinationCountTextBox.Text = combinationCount.ToString();

            Debug.Assert(this.combinationListBox.Items.Count == combinationCount);
        }

        #endregion

        //////////////////////////////////////////////////////////////////////////////// Function

        #region 항목 선택하기 - SelectItem<T>(itemList, selectionArray, resultList, selectionCount, firstItemIndex)

        /// <summary>
        /// 항목 선택하기
        /// </summary>
        /// <typeparam name="T">항목 타입</typeparam>
        /// <param name="itemList">항목 리스트</param>
        /// <param name="selectionArray">선택 배열</param>
        /// <param name="resultList">결과 리스트</param>
        /// <param name="selectionCount">선택 카운트</param>
        /// <param name="firstItemIndex">첫번째 항목 인덱스</param>
        private void SelectItem<T>(List<T> itemList, bool[] selectionArray, List<List<T>> resultList, int selectionCount, int firstItemIndex)
        {
            if(selectionCount == 0)
            {
                List<T> selectionList = new List<T>();

                for(int i = 0; i < itemList.Count; i++)
                {
                    if(selectionArray[i])
                    {
                        selectionList.Add(itemList[i]);
                    }
                }

                resultList.Add(selectionList);
            }
            else
            {
                for(int i = firstItemIndex; i < itemList.Count; i++)
                {
                    selectionArray[i] = true;

                    SelectItem(itemList, selectionArray, resultList, selectionCount - 1, i + 1);

                    selectionArray[i] = false;
                }
            }
        }

        #endregion
        #region 조합 리스트 구하기 - GetCombinationList<T>(itemList, selectionCount)

        /// <summary>
        /// 조합 리스트 구하기
        /// </summary>
        /// <typeparam name="T">항목 타입</typeparam>
        /// <param name="itemList">항목 리스트</param>
        /// <param name="selectionCount">선택 카운트</param>
        /// <returns>조합 리스트</returns>
        private List<List<T>> GetCombinationList<T>(List<T> itemList, int selectionCount)
        {
            bool[] selectionArray = new bool[itemList.Count];

            List<List<T>> resultList = new List<List<T>>();

            SelectItem<T>(itemList, selectionArray, resultList, selectionCount, 0);

            return resultList;
        }

        #endregion
        #region 조합 카운트 구하기 - GetCombinationCount(itemCount, selectionCount)

        /// <summary>
        /// 조합 카운트 구하기
        /// </summary>
        /// <param name="itemCount">항목 카운트</param>
        /// <param name="selectionCount">선택 카운트</param>
        /// <returns>조합 카운트</returns>
        private decimal GetCombinationCount(decimal itemCount, decimal selectionCount)
        {
            Debug.Assert(itemCount >= 0);
            Debug.Assert(selectionCount >= 0);
            Debug.Assert(itemCount >= selectionCount);

            decimal result = 1;

            for(int i = 1; i <= selectionCount; i++)
            {
                result *= itemCount - (selectionCount - i);
                result /= i;
            }

            return result;
        }

        #endregion
    }
}