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  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4.  
  5. static class Program
  6. {
  7.         public static void Main(string[] args)
  8.         {
  9.             var list1 = new int?[] { 1, 2, 3, 4, 5 };
  10.             var list2 = new int?[] { 3, 4, 5, 6, 7 };
  11.             var list3 = new int?[] { 6, 9, 9 };
  12.  
  13.             var lockstep = LockStepSequences(new[] { list1, list2, list3 });
  14.  
  15.             foreach (var step in lockstep)
  16.                 Console.WriteLine(string.Join("\t", step.Select(i => i.HasValue ? i.Value.ToString() : "null").ToArray()));
  17.         }
  18.  
  19.         public static IEnumerable<IEnumerable<T>> LockStepSequences<T>(this IEnumerable<IEnumerable<T>> sequences)
  20.         {
  21.             var iters = sequences
  22.                 .Select((s, index) => new { active=true, index, enumerator = s.GetEnumerator() })
  23.                 .ToArray();
  24.  
  25.             var isActive = iters.Select(it => it.enumerator.MoveNext()).ToArray();
  26.             var numactive = isActive.Count(flag => flag);
  27.  
  28.             try
  29.             {
  30.                 while (numactive > 0)
  31.                 {
  32.                     T min = iters
  33.                         .Where(it => isActive[it.index])
  34.                         .Min(it => it.enumerator.Current);
  35.  
  36.                     var row = new T[iters.Count()];
  37.  
  38.                     for (int j = 0; j < isActive.Length; j++)
  39.                     {
  40.                         if (!isActive[j] || !Equals(iters[j].enumerator.Current, min)) 
  41.                             continue;
  42.  
  43.                         row[j] = min;
  44.                         if (!iters[j].enumerator.MoveNext())
  45.                         {
  46.                             isActive[j] = false;
  47.                             numactive -= 1;
  48.                         }
  49.                     }
  50.                     yield return row;
  51.                 }
  52.             }
  53.             finally
  54.             {
  55.                 foreach (var iter in iters) iter.enumerator.Dispose();
  56.             }
  57.         }
  58. }
  59.  
  60.  
Success #stdin #stdout 0.06s 37288KB
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stdin
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Standard input is empty
stdout
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1	null	null
2	null	null
3	3	null
4	4	null
5	5	null
null	6	6
null	7	null
null	null	9
null	null	9
https://ideone.com/FuZIDy
language:
C# (gmcs 5.20.1)
created:
12 years ago
visibility:
secret

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