339. Nested List Weight Sum

题目：

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)

链接：

https://leetcode.com/problems/nested-list-weight-sum/?tab=Description

3/8/2017

注意list遍历时候用list.get(i)，还有每次每层的sum都是算得之下的值，不要把上层的sum值传入。

 1 /**
 2  * // This is the interface that allows for creating nested lists.
 3  * // You should not implement it, or speculate about its implementation
 4  * public interface NestedInteger {
 5  *
 6  *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
 7  *     public boolean isInteger();
 8  *
 9  *     // @return the single integer that this NestedInteger holds, if it holds a single integer
10  *     // Return null if this NestedInteger holds a nested list
11  *     public Integer getInteger();
12  *
13  *     // @return the nested list that this NestedInteger holds, if it holds a nested list
14  *     // Return null if this NestedInteger holds a single integer
15  *     public List<NestedInteger> getList();
16  * }
17  */
18 public class Solution {
19     public int depthSum(List<NestedInteger> nestedList) {
20         int sum = 0, depth = 1;
21         return nestedSum(nestedList, depth);
22     }
23     private int nestedSum(List<NestedInteger> nestedList, int depth) {
24         int sum = 0;
25         for(int i = 0; i < nestedList.size(); i++) {
26             if (nestedList.get(i).isInteger()) sum += nestedList.get(i).getInteger() * depth;
27             else {
28                 sum += nestedSum(nestedList.get(i).getList(), depth + 1);
29             }
30         }
31         return sum;
32     }
33 }

答案基本跟我的一致，区别是遍历得更加好。https://leetcode.com/articles/nested-list-weight-sum/

第25行：for (NestedInteger n : list)