allocateBooksJava

public class Solution {
    private boolean isPossible(ArrayList<Integer> A, int pages, int students) {
        int cnt = 0;
        int sumAllocated = 0; 
        for(int i = 0;i<A.size();i++) {
            if(sumAllocated + A.get(i) > pages) {
                cnt++; 
                sumAllocated = A.get(i);
                if(sumAllocated > pages) return false; 
            }
            else {
                sumAllocated += A.get(i);
            }
        }
        if(cnt < students) return true; 
        return false; 
    }
    public int books(ArrayList<Integer> A, int B) {
        if(B > A.size()) return -1; 
        int low = A.get(0); 
        int high = 0;
        for(int i = 0;i<A.size();i++) {
            high = high + A.get(i); 
            low = Math.min(low, A.get(i)); 
        }
        int res = -1; 
        while(low <= high) {
            int mid = (low + high) >> 1; 
            //cout << low << " " << high << " " << mid << endl; 
            if(isPossible(A, mid, B)) {
                res = mid; 
                high = mid - 1; 
            }
            else {
                low = mid + 1; 
            }
        }
        // return res -> this is also correct
        return low; 
    }
}