Question

can anyone help me how to write binary search program in c++ that return multiple index.For instance

if i have 124564.It should give the index of both for value 4 .

Answer 1

`Hey,

Note: Brother if you have any queries related the answer please do comment. I would be very happy to resolve all your queries.

Please note firstly your example is wrong. Binary search uses sorted array to find index. Also, if there are let's say 7 4's then program should return the first and last 4 index because all other would be in between since array is sorted.

#include<bits/stdc++.h>
using namespace std;
  
/* if x is present in arr[] then returns the index of
FIRST occurrence of x in arr[0..n-1], otherwise
returns -1 */
int first(int arr[], int low, int high, int x, int n)
{
if(high >= low)
{
int mid = low + (high - low)/2;
if( ( mid == 0 || x > arr[mid-1]) && arr[mid] == x)
return mid;
else if(x > arr[mid])
return first(arr, (mid + 1), high, x, n);
else
return first(arr, low, (mid -1), x, n);
}
return -1;
}
  
  
/* if x is present in arr[] then returns the index of
LAST occurrence of x in arr[0..n-1], otherwise
returns -1 */
int last(int arr[], int low, int high, int x, int n)
{
if (high >= low)
{
int mid = low + (high - low)/2;
if (( mid == n-1 || x < arr[mid+1]) && arr[mid] == x)
return mid;
else if (x < arr[mid])
return last(arr, low, (mid -1), x, n);
else
return last(arr, (mid + 1), high, x, n);
}
return -1;
}
  
// Driver program
int main()
{
int arr[] = {1, 2, 2, 2, 2, 3, 4, 7, 8, 8};
int n = sizeof(arr)/sizeof(int);
  
int x = 8;
cout<<"First Occurrence = "<<first(arr, 0, n-1, x, n);
cout<<"\nLast Occurrence = "<<last(arr, 0, n-1, x, n)<<endl;
  
return 0;
}

Kindly revert for any queries

Thanks.