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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 {index, enumerator = s.GetEnumerator()})
  23.                 .Where(it => it.enumerator.MoveNext())
  24.                 .ToArray();
  25.  
  26.             try
  27.             {
  28.                 for(var active = iters.ToList(); active.Any();)
  29.                 {
  30.                     T min = active.Min(it => it.enumerator.Current);
  31.                     var corresponding = active.Where(it => Equals(it.enumerator.Current, min));
  32.  
  33.                     yield return iters.Select((el, i) => corresponding.Any(it => it.index == i)
  34.                         ? el.enumerator.Current 
  35.                         : default(T));
  36.  
  37.                     active = active.Except(corresponding.Where(it => !it.enumerator.MoveNext())).ToList();
  38.                 }
  39.             }
  40.             finally
  41.             {
  42.                 foreach (var iter in iters) iter.enumerator.Dispose();
  43.             }
  44.         }
  45. }
  46.  
  47.  
Success #stdin #stdout 0.06s 37320KB
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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/H4gCoE
language:
C# (gmcs 5.20.1)
created:
11 years ago
visibility:
secret

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