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BinarySearch

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  1. // C++ program to implement recursive Binary Search
  2. #include <iostream>
  3.  
  4. using namespace std;
  5.  
  6.  
  7. // A recursive binary search function. It returns
  8. // location of x in given array arr[l..r] is present,
  9. // otherwise -1
  10.  
  11. int binarySearch(int arr[], int l, int r, int x)
  12. {
  13.  
  14.     if (r >= l) {
  15.  
  16.         int mid = l + (r - l) / 2;
  17.  
  18.  
  19.  
  20.         // If the element is present at the middle
  21.  
  22.         // itself
  23.  
  24.         if (arr[mid] == x)
  25.  
  26.             return mid;
  27.  
  28.  
  29.  
  30.         // If element is smaller than mid, then
  31.  
  32.         // it can only be present in left subarray
  33.  
  34.         if (arr[mid] > x)
  35.  
  36.             return binarySearch(arr, l, mid - 1, x);
  37.  
  38.  
  39.  
  40.         // Else the element can only be present
  41.  
  42.         // in right subarray
  43.  
  44.         return binarySearch(arr, mid + 1, r, x);
  45.  
  46.     }
  47.  
  48.  
  49.  
  50.     // We reach here when element is not
  51.  
  52.     // present in array
  53.  
  54.     return -1;
  55. }
  56.  
  57.  
  58.  
  59. int main(void)
  60. {
  61.   char choice;
  62.   char string;
  63.  
  64.     int arr[] = { 5, 10, 15, 20 ,25, 50, 65, 70, 90, 100 };
  65.  
  66.     int x;
  67.          cout << "input your choice" << endl << endl;
  68.          cin >> x;
  69.  
  70.     int n = sizeof(arr) / sizeof(arr[0]);
  71.  
  72.     int result = binarySearch(arr, 0, n - 1, x);
  73.  
  74.     (result == -1) ? cout << "Element is not present in array"
  75.  
  76.                    : cout << "Element is present at index " << result;
  77.  
  78.     return 0;
  79. }
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