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wockrad
wockrad wrote ...

2014/6/20

How many elements of a specific value in an array

wockrad wockrad

2014/6/20

#
Hey, sorry if this is a bit of a basic / stupid question but I'm trying to build a method using the built in java array utilities to find out how many elements of a specific value there are in an array. For example, if the array contained 4,4,4,6 and the argument was 4, I would want it to return 3. I thought I might be able to do it using the binarySearch method but even if I could get it to work it would probably be incredibly clunky and inefficient. I'm hoping there's a built in method for this like the binarySearch or sort ones but if there is one, I cant find it.
lordhershey lordhershey

2014/6/20

#
If the array is sorted you can use a binary search to find one of the instances of the '3', then you just count up and down until you hit non-3's There will be a linear element to this and your worst case running is big O of n. If you could make you array a giant string then you could use regular expressions to find all instances of a pattern, but that would take a lot longer than the first method. You could also do this, go through the array, enter the numbers as keys in a hash table, have the value being the number of times it was seen. Then you can query the hash table (HashMap) when ever you like.
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