LeetCode 339. Nested List Weight Sum（加权和）

原题网址：https://leetcode.com/problems/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 + 4*2 + 6*3 = 27)

方法：递归求和。

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