/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
 
    public static int binarySearch(int[] arr, int target) {
        int left = 0, right = arr.length;
        while (left < right) {
            int mid = (left + right) / 2;
            if (arr[mid] == target) return mid;
            else if (arr[mid] < target) left = mid + 1;
            else right = mid - 1;
        }
        return -1;
    }
 
 
	public static void main (String[] args) throws java.lang.Exception
	{
        // Test
        int[] arr = {1, 3, 5, 7, 9};
        int target = 5;
        int result = binarySearch(arr, target);
        System.out.println(result);
 
	}
}

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