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Topic: How to find subset in two a array (Read 1158 times) |
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nks
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How to find subset in two a array
« on: Aug 26th, 2011, 10:48am » |
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There are two arrays given N and M(larger). How to find wether N is subset of M, i.e All elements of N is available in M,
No hashing is to be used.
Is there any other way possible without using any extra array in O(N).
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| « Last Edit: Aug 27th, 2011, 9:10am by nks » |
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towr
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Re: How to find subset in two a array
« Reply #1 on: Aug 26th, 2011, 11:41am » |
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If M is smaller than N, as you stated, then N can't be a (proper) subset of M.
Assuming that was just a mistake, you could find whether the smaller set is a subset of the larger one in linear time if they're both sorted.
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nks
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Re: How to find subset in two a array
« Reply #2 on: Aug 27th, 2011, 9:16am » |
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Thanks TOWR for correction, Have corrected it, M is larger,
Sorting is known as O( N log N) excluding counting sort.
looking in O(N) with space O(1).
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| « Last Edit: Aug 27th, 2011, 9:17am by nks » |
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Hippo
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Re: How to find subset in two a array
« Reply #4 on: Sep 12th, 2011, 12:05pm » |
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Define encodding of array elements by positive integers (injection), map positive integer i to i-th prime (of precomputed subset of primes) (injection as well). Make products \PiN and \PiM of compound injections of arrray elements of N and of M.
Find their greatest common divisor. If it equals to \PiN you are done.
This solves problem when elements of N must be in M with their full multicity.
Yes, I am joking with infinit precision arithmetic with O(1) per operation.
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| « Last Edit: Sep 12th, 2011, 12:08pm by Hippo » |
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TenaliRaman
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Re: How to find subset in two a array
« Reply #5 on: Sep 12th, 2011, 12:16pm » |
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Sort the smaller array. Go over the larger array and check into the smaller array using binary search. This should be M log N. If N <<< M, the sorting cost and the logN search cost should be sufficiently small enough.
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