Nested List Weight Sum

Description

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

Example 1:

Input: the list [[1,1],2,[1,1]],
Output: 10.
Explanation:
four 1's at depth 2, one 2 at depth 1, 4 * 1 * 2 + 1 * 2 * 1 = 10

Example 2:

Input: the list [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
思路：dfs 按照深度带权求和

/**
 * // 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 helper(nestedList, 1);
    }

    public int helper(List<NestedInteger> nestedList, int depth){
        if (nestedList == null || nestedList.size() == 0)
            return 0;

        int sum = 0;
        for(NestedInteger ele : nestedList) {
            if (ele.isInteger()) {
                sum += ele.getInteger() * depth;
            } else {
                sum += helper(ele.getList(), depth + 1);
            }
        }

        return sum;
    }
}