abhinavawasthi's blog

unordered_map gives TLE? UMAP vs MAP
By abhinavawasthi, history, 2 years ago, In English

Yesterday, I have participated in codeforces round 773.

Was able to solve the first three questions during the contest, but my B and C submission got TLE on System Cases, do you know why? Just because I have used unordered_map instead of map.

I think, this is practical example to examine the diff btw unordered_map and map.

The same code with the same logic gives TLE, when using UMAP but got accepted, when using MAP.

1642B - Power Walking Submission with UMAP: submission:147440230

1642C - Great Sequence Submission with UMAP: submission:147426920

1642B - Power Walking Submission with MAP: submission:147497381

1642C - Great Sequence Submission with MAP: submission:147497320

One of my codeforces friends also told me about this, with a very good resource attached, you can check it.

Any suggestions are welcomed!

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Comments Comments (6)
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2 years ago, # |
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It's always better to use simple Map instead of Umap i guess

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    2 years ago, # ^ |
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    No Unordered map is faster than normal map.(for safety use custom hash function)

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2 years ago, # |
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I used unordered map with custom hash and got Ac.check my submission

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    2 years ago, # ^ |
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    So using custom hash reduces the the collision chances and the worst case happening probability even further ? From your implementation can it be used for only unsigned 32 or 64 bit int or can we make it even for strings ?

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2 years ago, # |
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Before making a blog on codeforces try googling "$your_subject codeforces". In your case google "unordered_map codeforces" and you will find many blogs on the subject. In particular there is this one that explains what is going and how to hack unordered_map.

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