LowerBound.java

// Modification of Binary Search
// Time Complexity: O(log n)
// Space Complexity: O(1)

import java.io.*;
import java.util.*;

class LowerBound {

    // function definition
    public static int findFirstOccurence(int[] arr, int target){
        int low=0, high=arr.length-1;
        int result = -1;

        while(low <= high){
            //to avoid overflow
            int mid = low + (high - low)/2;
            if(arr[mid] == target){
                result = mid;
                // traverse to the left side of an array
                high = mid - 1;
            }

            else if(arr[mid] > target){
                high = mid - 1;
            }

            else{
                low = mid + 1;
            }
        }
        return result;
    }


    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the number of elements in an array: ");
        int n = sc.nextInt();

        int arr[] = new int[n];

        System.out.println("Enter the array elements: ");
        for(int i=0; i<n; i++){
            arr[i] = sc.nextInt();
        }

        System.out.println("Enter the target element:");
        int target = sc.nextInt();

        // function calling
        int result = findFirstOccurence(arr, target);
        if(result == -1){
            System.out.println("Target element is not present in an array");
        }
        else{
            System.out.println("Target element first occurence is present at index: "+result);
        }
}
}
LowerBound.java
Displaying LowerBound.java.