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。

/**
 * // 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 sum = 0, depth = 1;
        return nestedSum(nestedList, depth);
    }
    private int nestedSum(List<NestedInteger> nestedList, int depth) {
        int sum = 0;
        for(int i = 0; i < nestedList.size(); i++) {
            if (nestedList.get(i).isInteger()) sum += nestedList.get(i).getInteger() * depth;
            else {
                sum += nestedSum(nestedList.get(i).getList(), depth + 1);
            }
        }
        return sum;
    }
}

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)