Thread: Hello everybody I need some help with a homework problem dealing with arrays and binary searches

I am very new to Java and this is my first time posting here, and I need some help solving this problem. Whenever I input a number it returns the index number in the ordered array, but when certain numbers (like 62, 68, 96) are inputted, the return is either the wrong index number or an error appears in the console. This may be an easy fix but I am completely stumped, and any help would be appreciated

import java.util.*;
import java.lang.*;
import java.io.*;
 
// The main method must be in a class named "Main".
class Main {
 
    // Literal 11 Element Array 
    static int[] _arr = {96, 61, 18, 85, 24, 62, 45, 3, 68, 57, 78};
 
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int arg = in.nextInt();
        PrintLine("Console Input: " + arg);
 
        OutputArray(_arr);
        Arrays.sort(_arr);
        OutputArray(_arr);
 
        int _cnt = _arr.length;
        int[] arr = Arrays.copyOfRange(_arr, 0, _cnt);
        int idx = BinarySearch(_arr, arg);
 
        PrintLine("Index: " + idx + "; Value: " + _arr[idx]);
    }
 
    static int BinarySearch(int[] arr, int value){
        return BinarySearch(arr, value, 0);
    }
 
    static int BinarySearch(int[] arr, int value, int idxOff){
        int len = arr.length;
        int retIdx = -1;
 
        if(len == 2){
            if(arr[0]== value){
                retIdx = idxOff;
            } else if(arr[1] == value) {
                retIdx = idxOff;
            }
        } else {
            int max = arr.length-1;
            int midIdx = max/2;
            System.out.println("Mid Idx: " + midIdx + "; Max Idx: " + max + "; Index Offset: " + idxOff + "; Array: " + Arrays.toString(arr));
            System.out.println("the length is: " + len);
 
            if(value == arr[midIdx]) {
                retIdx = midIdx;
            } else {
                if(value < arr[midIdx]){
                    int[] newArray = Arrays.copyOfRange(arr, 0, midIdx);
 
                    retIdx = BinarySearch(newArray, value);
                } else if(arr[midIdx] < value){
                    int[] newArray = Arrays.copyOfRange(arr, midIdx, max);
                    idxOff += midIdx;
 
                    retIdx = BinarySearch(newArray, value, idxOff);
                }
            }
        }
 
        return retIdx;
 
    }
 
    static void OutputArray(String[] arr){
        PrintLine("Array: " + Arrays.toString(arr));
    }
    static void OutputArray(int[] arr){
        PrintLine("Array: " + Arrays.toString(arr));
    }
 
    static void PrintLine(String msg){
        System.out.println(msg);
    }
}

Absolutely:

Correct output
3
Console Input: 3
Array: [96, 61, 18, 85, 24, 62, 45, 3, 68, 57, 78]
Array: [3, 18, 24, 45, 57, 61, 62, 68, 78, 85, 96]
Mid Idx: 5; Max Idx: 10; Index Offset: 0; Array: [3, 18, 24, 45, 57, 61, 62, 68, 78, 85, 96]
Mid Idx: 2; Max Idx: 4; Index Offset: 0; Array: [3, 18, 24, 45, 57]
Index: 0; Value: 3

Wrong index
62
Console Input: 62
Array: [96, 61, 18, 85, 24, 62, 45, 3, 68, 57, 78]
Array: [3, 18, 24, 45, 57, 61, 62, 68, 78, 85, 96]
Mid Idx: 5; Max Idx: 10; Index Offset: 0; Array: [3, 18, 24, 45, 57, 61, 62, 68, 78, 85, 96]
Mid Idx: 2; Max Idx: 4; Index Offset: 5; Array: [61, 62, 68, 78, 85]
Index: 0; Value: 3

Console error
96
Console Input: 96
Array: [96, 61, 18, 85, 24, 62, 45, 3, 68, 57, 78]
Array: [3, 18, 24, 45, 57, 61, 62, 68, 78, 85, 96]
Mid Idx: 5; Max Idx: 10; Index Offset: 0; Array: [3, 18, 24, 45, 57, 61, 62, 68, 78, 85, 96]
Mid Idx: 2; Max Idx: 4; Index Offset: 5; Array: [61, 62, 68, 78, 85]
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1
at Main.main(Main.java:24)

Going down the list of numbers in the array, this is what they return:

(input, index return, value return)

3, index 0, value: 3
18, index 1, value: 18
24, index 2, value: 24
45, index, 3, value: 45
57, returns error
61, index 5, value: 61
62, index 0, value: 3
68, index 2, value: 24
78, index 8, value: 78
85, returns error
96, returns error

I have tried printing some values for debugging but I am not sure what exactly I should be printing haha I am super new to Java sorry

Sorry for cross-posting. My professor said that there was a line or multiple lines of code wrong with the original code, and said that the bulk of the original code cannot change. I have been looking and playing with different variables and stuff but I still have no idea what the solution is. The main goal is to just have the input 62 output the correct index number. I believe it has something to do with the index offset but idk what to do with that. My thought is that the index numbers are repeating and not properly adjusting to when the index offset is on the last half of the index (61, 62, 68, 78, 85, 96). I could be completely wrong but that's just my guess.

While checking over the code and printing out different things I noticed an integer called "int value" at line 27 being used with the BinarySearch. I don't see a previous naming of int value and I was wondering what that could be. Is "value" a type of "filler" declaration or something like that for a variable?

This is the code for where "value" is being used a parameter:


This is the first time is has been used and it was not declared before. Does it need to be declared previously or is it acceptable to be used as a parameter for a binarySearch without a declaration?

 static int binarySearch(int[] arr, int value){  //first time using value
        return binarySearch(arr, value, 0);
    }
 
    static int binarySearch(int[] arr, int value, int idxOff){
        int len = arr.length;
        int retIdx = -1;
 
        if(len == 2){
            if(arr[0]== value){
                retIdx = idxOff;
            } else if(arr[1] == value) {
                retIdx = idxOff+1;
            }
        } else {
            int max = arr.length-1;
            int midIdx = max/2;
            System.out.println("Mid Idx: " + midIdx + "; Max Idx: " + max + "; Index Offset: " + idxOff + "; Array: " + Arrays.toString(arr));
 
            if(value == arr[midIdx]) {
                retIdx = midIdx;
            } else {
                if(value < arr[midIdx]){
                    int[] newArray = Arrays.copyOfRange(arr, 0, midIdx);
 
                    retIdx = binarySearch(newArray, value);
                } else if(arr[midIdx] < value){
                    int[] newArray = Arrays.copyOfRange(arr, midIdx, max);
                    idxOff += midIdx;
 
                    retIdx = binarySearch(newArray, value, idxOff);
                }
            }