339. Nested List Weight Sum

Given a nested list of integers, return the sum of all integers in the list weighted by their depth.

Each element is either an integer, or a list -- whose elements may also be integers or other lists.

Example 1:

Input: [[1,1],2,[1,1]]
Output: 10 
Explanation: Four 1's at depth 2, one 2 at depth 1.

Example 2:

Input: [1,[4,[6]]]
Output: 27 
Explanation: One 1 at depth 1, one 4 at depth 2, and one 6 at depth 3; 1 + 4*2 + 6*3 = 27.

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * class NestedInteger {
 *   public:
 *     // Constructor initializes an empty nested list.
 *     NestedInteger();
 *
 *     // Constructor initializes a single integer.
 *     NestedInteger(int value);
 *
 *     // 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;
 *
 *     // Set this NestedInteger to hold a single integer.
 *     void setInteger(int value);
 *
 *     // Set this NestedInteger to hold a nested list and adds a nested integer to it.
 *     void add(const NestedInteger &ni);
 *
 *     // 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;
 * };
 */

// DFS
int helper(vector<NestedInteger>& nestedList, int depth) {
    int res = 0;
    for (NestedInteger& ni : nestedList) {
        res += ni.isInteger() ? (ni.getInteger() * depth) : helper(ni.getList(), depth + 1);
    }
    return res;
}
int depthSum(vector<NestedInteger>& nestedList) { // time: O(n); space: O(n)
    return helper(nestedList, 1);
}

// BFS similar to tree level order traversal
int depthSum(vector<NestedInteger>& nestedList) { // time: O(n); space: O(n)
    if (nestedList.empty()) return 0;
    int res = 0, level = 1;
    queue<NestedInteger> q;
    for (NestedInteger& ni : nestedList) q.push(ni);
    while (!q.empty()) {
        for (int k = q.size() - 1; k >= 0; --k) {
            NestedInteger ni = q.front(); q.pop();
            if (ni.isInteger()) {
                res += ni.getInteger() * level;
            } else {
                for (NestedInteger& n : ni.getList()) q.push(n);
            }
        }
        ++level;
    }
    return res;
}