Triangle, C# - rextester

Triangle

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        static void log(int[] arr)
        {
            //log("Array size: " + arr.Length);
            //log();
            Console.Write("[" + String.Join(" ", arr) + "]");
        }
        
        // get all unique/distinct permutations
        //
        // var arr = new int[] { 1, 2, 3, 4, 5 };
        // var result = GetAllUniquePermutations(arr, 2);
        // 
        // count = 2 =>
        // 1, 2
        // 1, 3
        // 1, 4
        // 1, 5
        //
        // 2, 3
        // 2, 4
        // 2, 5
        //
        // 3, 4
        // 3, 5
        //
        // 4, 5
        static IEnumerable<IEnumerable<T>> GetAllUniquePermutations<T>(IEnumerable<T> items, int count){
            int i = 0;
            foreach (var item in items){
                if (count == 1){
                    yield return new T[] { item };
                }else{
                    foreach (var result in GetAllUniquePermutations(items.Skip(i + 1), count - 1))
                    {
                        yield return new T[] { item }.Concat(result);
                    }
                }
                i++;
            }
        }
        
        public static void Main(string[] args)
        {
            var array = Enumerable.Range(1, 5).ToArray();
            Console.WriteLine("Original array:");
            log(array);
            Console.WriteLine();
            Console.WriteLine();
            
            var allUniquePermutations = GetAllUniquePermutations(array, 3);
            Console.WriteLine("All possible permutations:");
            foreach(var permutation in allUniquePermutations){
                log(permutation.ToArray());
                Console.WriteLine();
            }
        }
    }
}


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