Allocate Books

Given an array of integers A of size N and an integer B.

The College library has N books. The ith book has A[i] number of pages.

You have to allocate books to B number of students so that the maximum number of pages allocated to a student is minimum.

A book will be allocated to exactly one student.
Each student has to be allocated at least one book.
Allotment should be in contiguous order, for example: A student cannot be allocated book 1 and book 3, skipping book 2.
Calculate and return that minimum possible number.

NOTE: Return -1 if a valid assignment is not possible.

A = [12, 34, 67, 90]
B = 2

Output:
113


bool isAllocationPossible(int barrier, vector<int>&arr, int totalStudents){
    int n=arr.size();
    int allocatedStudent=1;
    int pages=0;
    for(int i=0;i<n;i++){
        if(arr[i]>barrier)return false;
        if(pages + arr[i]>barrier){
            allocatedStudent+=1;
            // pages=0;
            pages=arr[i];
        }
        else{
            pages+=arr[i];
        }
    }
    if(allocatedStudent > totalStudents){
        return false;
    }
    return true;
}


int Solution::books(vector<int> &A, int B) {
    int mini=INT_MAX;
    int sum=0;
    int n=A.size();
    if(n<B)return -1;//very important to check this condition
    for(int i=0;i<n;i++){
        sum+=A[i];
        mini=min(mini,A[i]);
    }
    int low=mini;
    int high=sum;
    int res=-1;
    while(low<=high){
        int mid= low + (high - low )/2;
        if(isAllocationPossible(mid,A,B)){
            res=mid;
            high= mid-1;
        }
        else{
            low=mid+1;
        }
    }
    return res;
    
}