Allocate minimum number of pages

Allocate minimum number of pages

Allocate minimum number of pages

You are given N number of books. Every i^th book has P_i number of pages. 
You have to allocate books to M number of students. There can be many ways or permutations to do so. In each permutation one of the M students will be allocated the maximum number of pages. Out of all these permutations, the task is to find that particular permutation in which the maximum number of pages allocated to a student is minimum of those in all the other permutations, and print this minimum value.

Each book will be allocated to exactly one student. Each student has to be allocated atleast one book.

Note: Return -1 if a valid assignment is not possible, and allotment should be in contiguous orde

For each test case, output a single line containing minimum number of pages each student has to read for corresponding test case.

#include <bits/stdc++.h>
#define ll long long int 
using namespace std;
bool findsol(int a[],int n,int m ,ll ans)
{
    
    int i=0,j=0;
    ll sump=0;//assign the maximum pages
          //that can read which less than equal to ans
   
    while(i<n)
    {
     if(sump+a[i]<=ans)
     {
         sump+=a[i++];
     }else{
         ++j;
         sump=0;
     }
    //No of sudent greater than m to assign all book return false
     if(j>=m)return false;
    }
// at last all check and student equal to  m;
    return true;
   
}
// finding ans with binary search
ll binarysearch(int a[],int n,int m,ll end ,ll start)
{
    ll ans=a[n-1];
    while(start<=end)
    {
        ll mid=(start+end)/2;
        if(findsol(a,n,m,mid))
        {
// if mid is valid then assign this to answer
//change the end to mid-1 so minimize the answer till start ==end
            ans=mid;
            end=mid-1;
        }else{
//if mid is not valid then search  between mid+1 and end
            start=mid+1;
        }
       
    }
    return ans;
}
int main() {
    //code
    int t;
    cin>>t;
    while(t--)
    {

       int  n,m;
       ll sum=0;
        cin>>n;
        int a[n];

        for(int i=0;i<n;++i)
        {
            cin>>a[i];
            sum+=a[i];
        }
       
        cin>>m;
       //if no of sudent is greater than book then return -1 as at least one book
       // is allocate every one student
        if(m>n)
        cout<<-1<<endl;
          else if(n==m){
      //if no of student is equal to no of book then return book with  maximum page
            cout<<*max_element(a,a+n)<<endl;
            }
            else{
            cout<<binarysearch(a,n,m,sum,a[0])<<endl;
        }
       
       
    }
    return 0;
}