Java arrays.binary search multiple matches?

Question

I need to find all elements in sorted array with Arrays.binarySearch method. I want to iterate binary search in lowerbound = pos + 1 (pos is previous match), but binarySearch is not guaranteed to return first match (min match index)?

How can I make this?

Eran · Accepted Answer · 2015-03-22 11:06:25Z

9

You can easily use the result of binarySearch to get all the matches :

long[] sortedArr = ...
int index = Arrays.binarySearch (sortedArr, value);
int first = index;
int last = index;
if (index >= 0) {
    while (first > 0 && sortedArr[first-1] == value)
        first--;
    while (last < sortedArr.length - 1 && sortedArr[last+1] == value)
        last++;
}

After you run this code, the indices between first and last (inclusive) are all the indices that contain the searched value.

answered Mar 22, 2015 at 11:06

Eran

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2 Comments

user2010633 Over a year ago

I make it like you. Just I want know, maybe I can iterate this in 'one-line' style.

Andreas Over a year ago

looping without braces won't pass code review around here.

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