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  1. import java.util.*;
  2.  
  3. class FindFirstOne {
  4.     public static void main(String[] args) {
  5.         Scanner sc = new Scanner(System.in);
  6.  
  7.         // Input size of the array
  8.         System.out.print("Enter the size of the array: ");
  9.         int n = sc.nextInt();
  10.  
  11.         // Input elements of the array
  12.         int[] arr = new int[n];
  13.         System.out.println("Enter the elements (0s and 1s only): ");
  14.         for (int i = 0; i < n; i++) {
  15.             arr[i] = sc.nextInt();
  16.         }
  17.  
  18.         int firstOccurrence = findFirstOne(arr, n);
  19.  
  20.         if (firstOccurrence != -1) {
  21.             System.out.println("First occurrence of 1 is at index: " + firstOccurrence);
  22.         } else {
  23.             System.out.println("1 is not present in the array.");
  24.         }
  25.     }
  26.  
  27.     public static int findFirstOne(int[] arr, int n) {
  28.         int start = 0;
  29.         int end = n - 1;
  30.         int maybeFirst1 = -1;
  31.  
  32.         while (start <= end) {
  33.             int mid = start + (end - start) / 2; // Correctly calculate mid
  34.  
  35.             if (arr[mid] == 0) {
  36.                 start = mid + 1; // Move right if 0 is found
  37.             } else {
  38.                 maybeFirst1 = mid; // Found a 1, keep track
  39.                 end = mid - 1; // Move left to find the first occurrence
  40.             }
  41.         }
  42.  
  43.         return maybeFirst1; // Return the index of the first occurrence of 1
  44.     }
  45. }
  46.  
Success #stdin #stdout 0.15s 58912KB
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stdin
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5
0 0 1 1 1
stdout
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Enter the size of the array: Enter the elements (0s and 1s only): 
First occurrence of 1 is at index: 2
https://ideone.com/UC7FHg
language:
Java (HotSpot 12)
created:
20 hours ago
visibility:
public

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