Allocate Books

• Time : $O(nlog(INT_MAX))$
• Space : $O(1)$

bool helper(vector<int>& A, long long mi, long long B) {
    long long now = 0, count = 1;
    for(int i = 0; i < A.size(); i++) {
        if(now + A[i] <= mi) now += A[i];
        else now = A[i], count += 1;
    }
    return count <= B;
}
int Solution::books(vector<int> &A, int B) {
    if(A.size() < B) return -1;
    long long l = *max_element(begin(A), end(A)), r = INT_MAX, res = INT_MAX;
    while(l <= r) {
        long long m = l + (r - l) / 2;
        bool pass = helper(A,m,B);
        if(pass) {
            r = m - 1;
            res = m;
        } else l = m + 1;
    }
    return res == INT_MAX ? -1 : res;
}