LeetCode: Nested List Weight Sum

LeetCode: 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:

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 + 42 + 63 = 27)

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/**
 * // 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 {
     public int depthSum(List<NestedInteger> nestedList) {
        return process(nestedList, 1);

    }

    private int process(List<NestedInteger> list, int depth) {
        if (list == null || list.isEmpty()) {
            return 0;
        }

        int sum = 0;
        for (NestedInteger ni : list) {
            if (ni.isInteger()) {
                sum += depth * ni.getInteger();
            } else {
                sum += process(ni.getList(), depth + 1);
            }
        }

        return sum;
    }
}