GeeksforGeeks » Algorithms
Check repitition of number in an Array
(6 posts)-
Given an array , say abc[10]..
10 numbers are entered by user..
only one number is repeated..
we have to output that repeated number...
Please help me out in finding a nice algorithm for this. -
Declare another array Hash[], and do the following steps.
i from 1 to 10 of abc,
{
if (Hash[abc[i]]==0) Hash[abc[i]]+=1;
else abc[i] is the answer.
} -
if 'n' = number of first n natural numbers , then the repeated number can be found as
sum of n numbers(with the repated number) - sum of first(n-1) numbers = repeated number
eg: if n =5 then a[5] will have 4 natural numbers = 0,1,2,3,4. Lets say 3 is repeated. then:
the input array has values : 1,2,3,3,4 , then applying the above algo will give:
(1+2+3+4+3) - (sum of first 4 natural numbers(given n=5))
=> 13-10 = 3
3 is the repeated number.you can try with any value of n.
This applies only if the n is a sequence of n natural numbers. Let me know if the question is quoted otherwise.
Thanks -
thanx to all of you !!! :)
-
@devan: what would be size of Hash[] array??
-
If there is no relation between the numbers (like not being consecutive), then sort the array(n log n) and then do a traverse through the array O( n).
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