Nested List Weight Sum — C++

// Time:  O(n)
// Space: O(h)

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * class NestedInteger {
 *   public:
 *     // Return true if this NestedInteger holds a single integer, rather than a nested list.
 *     bool isInteger() const;
 *
 *     // Return the single integer that this NestedInteger holds, if it holds a single integer
 *     // The result is undefined if this NestedInteger holds a nested list
 *     int getInteger() const;
 *
 *     // Return the nested list that this NestedInteger holds, if it holds a nested list
 *     // The result is undefined if this NestedInteger holds a single integer
 *     const vector<NestedInteger> &getList() const;
 * };
 */
class Solution {
public:
    int depthSum(vector<NestedInteger>& nestedList) {
        return depthSumHelper(nestedList, 1);
    }

private:
    int depthSumHelper(const vector<NestedInteger>& nestedList, int depth) {
        int sum = 0;
        for (const auto& list : nestedList) {
            if (list.isInteger()) {
                sum += list.getInteger() * depth;
            } else {
                sum += depthSumHelper(list.getList(), depth + 1);
            }
        }
        return sum;
    }
};