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:

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)

/**
 * // 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) {
        int res = 0;
        for(NestedInteger ni : nestedList){
            res += weight(ni, 1);
        }
        return res;
    }

    private int weight(NestedInteger ni, int w){
        if(ni.isInteger()){
            return ni.getInteger() * w;
        }
        int res =0;
        for(NestedInteger nni : ni.getList()){
            res += weight(nni, w+1);
        }
        return res;
    }
}

a clearer solution.

 public class Solution {
    public int depthSum(List<NestedInteger> nestedList) {
        return sum(nestedList, 1);

    }
    private int sum(List<NestedInteger> nl, int depth){
        int sum = 0;
        for(NestedInteger ni : nl){
            if(ni.isInteger()){
                sum += ni.getInteger() * depth;
            }else{
                sum += sum(ni.getList(), depth+1);
            }
        }
        return sum;
    }

}