Capacity To Ship Packages Within B Days

• Time : $O(nlogsum(A))$
• Space : $O(1)$

int helper(vector<int>& A, int k) {
    int res = 1, now = 0;
    for(auto a : A) {
        if(now + a > k) {
            now = a;
            res += 1;
        } else now += a;
    }
    return res;
}
int Solution::solve(vector<int> &A, int B) {
    int l = *max_element(begin(A), end(A)), r = INT_MAX, res = INT_MAX;
    while(l <= r) {
        int m = l + (r - l) / 2;
        int d = helper(A,m);
        if(d <= B) res = min(res, m);
        if(d > B) l = m + 1;
        else r = m - 1;
    }
    return res;
}