Range Addition — C++

// Time:  O(k + n)
// Space: O(1)

class Solution {
public:
    vector<int> getModifiedArray(int length, vector<vector<int>>& updates) {
        vector<int> result(length, 0);

        for (const auto& update: updates) {
            result[update[0]] += update[2];
            if (update[1] + 1 < length) {
                result[update[1] + 1] -= update[2];
            }
        }

        for (int i = 1; i < length; ++i) {
            result[i] += result[i - 1];
        }

        return result;
    }
};