leetcode Nested List Weight Sum

https://leetcode.com/problems/nested-list-weight-sum/

Problem

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:
Given the list [[1,1],2,[1,1]], return 10. (four 1’s at depth 2, one 2 at depth 1)

Example 2:
Given the list [1,[4,[6]]], return 27. (one 1 at depth 1, one 4 at depth 2, and one 6 at depth 3; 1 + 4*2 + 6*3 = 27)

Solution

A recursive implementation and looks like back tracking on depth.

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * public interface NestedInteger {
 *
 *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
 *     public boolean isInteger();
 *
 *     // @return the single integer that this NestedInteger holds, if it holds a single integer
 *     // Return null if this NestedInteger holds a nested list
 *     public Integer getInteger();
 *
 *     // @return the nested list that this NestedInteger holds, if it holds a nested list
 *     // Return null if this NestedInteger holds a single integer
 *     public List<NestedInteger> getList();
 * }
 */
public class Solution {
    int depth = 1;
    int sum = 0;
    public int depthSum(List<NestedInteger> nestedList) {
        for(NestedInteger n : nestedList) {
            if(n.isInteger())
                sum += n.getInteger() * depth;
            else {
                depth++;
                depthSum(n.getList());
                depth--;
            }
        }
        return sum;
    }
}