Sell Diminishing-Valued Colored Balls — C++

// Time:  O(nlogm), m is the max of inventory, n is the size of inventory
// Space: O(1)

class Solution {
public:
    int maxProfit(vector<int>& inventory, int orders) {
        static const int MOD = 1e9 + 7;

        int left = 1, right = *max_element(cbegin(inventory), cend(inventory));
        while (left <= right) {
            const auto mid = left + (right - left) / 2;
            if (!check(inventory, orders, mid)) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        uint64_t result = 0;
        for (const auto& cnt : inventory) {
            if (cnt >= left) {
                result = (result + (uint64_t(left + cnt) * (cnt - left + 1) / 2) % MOD) % MOD;
            }
        }
        // assert(orders - count(inventory, left) >= 0);
        return (result + uint64_t(left - 1) * (orders - count(inventory, left)) % MOD) % MOD;
    }
            
private:
    int count(const vector<int>& inventory, int x) {
        static const int MAX_ORDERS = 1e9;

        int result = 0;
        for (const auto& cnt : inventory) {
            if (cnt >= x) {
                if (result >= (MAX_ORDERS + 1) - (cnt - x + 1)) {
                    result = MAX_ORDERS + 1;
                    break;
                }
                result += cnt - x + 1;
            }
        }
        return result;
    }

    bool check(const vector<int>& inventory, int orders, int x) {
        return count(inventory, x) > orders;
    }
};