Java/binarySearch

Question

Does it suppose to return index of first occurrence for thr binarySearch method?
What is the problem with this code?
It returns the 2 for 5
int arr [] = {3,5,6,9,10,6};
Arrays.sort(arr);
System.out.println (arr, 5);

Answer 1

MUHAMMED AYDIN

It is true that the method returns the index of first occurence. But the algorithm works not linear.

If you study the example in the binary search lesson you will understand it.

Answer 2

Yes it return index where the input found...
In your case, It returns 1 not 2, since index starts from 0..
Where is code?

Answer 3

Hello MUHAMMED AYDIN

Please share your complete code. Thanks.

Answer 4

MUHAMMED AYDIN

It shows me 1 as output which is correct.

after sorting: 3, 5, 6, 6, 9, 10
index starts with 0.
So 5 is at index 1.

Answer 5

MUHAMMED AYDIN
Same. Just run the code:

https://code.sololearn.com/c3J9v2LwB1Sk/?ref=app

Answer 6

MUHAMMED AYDIN
I changed the code. Output is 2 which is also correct.

https://code.sololearn.com/c3J9v2LwB1Sk/?ref=app

after sorting: 3, 5, 5, 6, 6, 9, 10
one 5 at 1 and another at 2.

It depends on the implementation of binary search if you find the 5 at 1 or 5 at 2.

About binary search in general:
https://www.sololearn.com/learn/664/?ref=app

Answer 7

Binary search method searches key in the array mid position, every time. Since array passed should be in sorted order. So if search not match at mid position, it take search in either left array or in right array iteratively so if elements contains doublicates then no guarantee for index which one picked.. If it not in sorted also, same undefined behavior happens...

Check this in above example by running it for 5 by adding more elements same..
Binary search method searches key in the array mid position,
If it take linear search, then it return first occurrence.

int arr [] = {3,5,5,5,6,6,9,9,10};
Arrays.sort(arr);
System.out.println(Arrays.binarySearch(arr, 5));
Run same with adding some more elements, then answer may vary..

Answer 8

Could you please run the code? I don't know what I am doing wrongly, but I am getting 2 as return

Answer 9

Where is your code...? How can I run it, without sharing?

Answer 10

public static void main (String [] args) {
int arr [] = {3,5,6,9,10,6};
Arrays.sort(arr);
System.out.println (Arrays.binarySearch(arr, 5));
}

Answer 11

Can you try for this one, I shared the wrong one?.
public static void main (String [] args) {
int arr [] = {3,5,6,9,10 };
Arrays.sort(arr);
System.out.println (Arrays.binarySearch(arr, 5));
}

Answer 12

I did for this one, sorry one more time
public static void main (String [] args) {
int arr [] = {3,5,6, 5,9,10,6 };
Arrays.sort(arr);
System.out.println (Arrays.binarySearch(arr, 5));
}

Answer 13

So assuming binarySearch given index of first occurrence is not certain?