CODEWITHSUNDEEP
javaarraysalgorithmmath
Van Minh Nhon TRUONG
Van Minh Nhon TRUONG

Reputation: 99

why doesn't binarySearch method return the correct result?

Recently I am working on arrays in Java and I needed to use the method binarySearch(arr, v) in Arrays class to search the index of value v in the array arr if found.

Then I do some tests with some different arrays. When I try to search value 4 in the array {4, 3, 2, 1} I found -5.

Would someone can explain that please ?

You can check here http://tpcg.io/kibBmw

The code is below:

int[] arr   = {4, 3, 2, 1};
System.out.println(Arrays.binarySearch(arr, 4));

-5

Upvotes: 0

Views: 69

Answers (3)

Nishant Middha
Nishant Middha

Reputation: 302

For using standard binary search algorithm your input array must be in increasing value order otherwise you will get unexpected results.

Upvotes: 0

Andronicus
Andronicus

Reputation: 26076

Just look at the javadoc. You need to have a sorted array to use this method. You can do the following:

Arrays.sort(arr);
Arrays.binarySearch(arr, 4)

Upvotes: 1

Ruslan
Ruslan

Reputation: 6300

You should do Arrays.sort(arr); before the binary search. From the documentation for Arrays.binarySearch:

Searches the specified array of ints for the specified value using the binary search algorithm. The array must be sorted (as by the sort(int[]) method) prior to making this call. If it is not sorted, the results are undefined.

Upvotes: 3

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