first&last_occurence.cpp

/*
   Program to find first and last occurence(index) of the specified element in an entered array
      also helpfull to find no of occurences of specified element by performing the following operation => { (last occ) - (first occ) + 1 }
*/

#include<bits/stdc++.h>
using namespace std;

scanarray(int ar[], int n){
      cout<<"Enter elements in array\n";
      for(int i=0; i<n; i++){
            cin>>*(ar+i);
      }
}

printarray(int ar[], int n){
      for(int i=0; i<n; i++){
            cout<<*(ar+i)<<" ";
      }
}

frmstart(int ar[], int n, int key){
      int s = 0, e = n-1, mid, ans;
      mid = s + (e-s)/2;
      while(s<=e){
            if(ar[mid]==key){
                  ans=mid;
                  e = mid-1;
            }
            else if(ar[mid]>key){
                  e = mid-1;
            }
            else if(ar[mid]<key){
                  s = mid+1;
            }

            mid = s + (e-s)/2;
      }
      return ans;
}

frmend(int ar[], int n, int key){
      int s = 0, e = n-1, mid, ans;
      mid = s + (e-s)/2;
      while(s<=e){
            if(ar[mid]==key){
                  ans=mid;
                  s = mid+1;
            }
            else if(ar[mid]>key){
                  e = mid-1;
            }
            else if(ar[mid]<key){
                  s = mid+1;
            }

            mid = s + (e-s)/2;
      }
      return ans;
}

int main(){
      int *ar, n, key;
      cout<<"Enter size of array\n";
      cin>>n;
      ar = (int*)malloc(n*sizeof(int));
      
      scanarray(ar, n);
      cout<<"Initial array\n";
      printarray(ar, n);
      cout<<"\nEnter key value\n";
      cin>>key;
      
      pair<int, int> p;
      p.first = frmstart(ar, n, key);
      p.second = frmend(ar, n, key);
      cout<<"first occuring index of key = "<<p.first<<endl;
      cout<<"last occuring index of key = "<<p.second<<endl;
      
      return 0;
}