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Asked: 2026-05-16T01:10:01+00:00

Actually, this is not specific to SQL, and I doubt conversation pattern is the

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Actually, this is not specific to SQL, and I doubt “conversation pattern” is the correct name, but I could not think of a better caption.

To simplify, imagine you got a vast stream of ints. The task is to detect an A.{1;max_n}A pattern: An int satisfies the pattern if it is followed by n (> 0) other ints, then the original int again, while n <= max_n.

Example:

...
1
4 <--
7 \
3  > n = 3
3 /
4 <--
2
...

Here, the int 4 is repeated with 3 arbitrary ints in-between, so for max_n <= 3 the pattern is satisfied for the value 4.

The question is, how can I detect which integers in the huge dump of data follow this pattern? I’m mostly interested in the algorithm itself, but an example in SQL or C# would be welcome, too.

The naive idea I came up with is to first gather a list or all distinct ints, then check the pattern in a straightforward way for each of them, but that would lead to a performance bottleneck.

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1 Answer

  1. Editorial Team

    You can hold some dictionary (C#) or map (C++) structure where will be saved position of first occurrence of numbers.

    Then for every number you should check if it present in map. If yes – you should compare position difference with maximum position difference occurred before. Otherwise you should save the number and its position in map.

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