_364_NestedListWeightSumII.java

package leetcode_1To300;

import java.util.LinkedList;
import java.util.List;

/**
 * 本代码来自 Cspiration，由 @Cspiration 提供
 * 题目来源：http://leetcode.com
 * - Cspiration 致力于在 CS 领域内帮助中国人找到工作，让更多海外国人受益
 * - 现有课程：Leetcode Java 版本视频讲解（1-900题）（上）（中）（下）三部
 * - 算法基础知识（上）（下）两部；题型技巧讲解（上）（下）两部
 * - 节省刷题时间，效率提高2-3倍，初学者轻松一天10题，入门者轻松一天20题
 * - 讲师：Edward Shi
 * - 官方网站：https://cspiration.com
 * - 版权所有，转发请注明出处
 */
public class _364_NestedListWeightSumII {
    /**
     * 364. Nested List Weight Sum II
     * 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.

     Different from the previous question where weight is increasing from root to leaf, now the weight is defined from bottom up. i.e., the leaf level integers have weight 1, and the root level integers have the largest weight.

     Example 1:
     Given the list [[1,1],2,[1,1]], return 8. (four 1's at depth 1, one 2 at depth 2)

     Example 2:
     Given the list [1,[4,[6]]], return 17.
     (one 1 at depth 3, one 4 at depth 2, and one 6 at depth 1; 1*3 + 4*2 + 6*1 = 17)

     DFS 2 + DFS(2, Nest)
       DFS 2 +

     nextList : 1, 1, 1, 1

     res = 2 + 2 + 4
        dfs(next, 2) res = 2 + 4

     time : O(n);
     space : O(n);
     * @param nestedList
     * @return
     */
    public int depthSumInverse(List<NestedInteger> nestedList) {
        if (nestedList == null) return 0;
        return helper(nestedList, 0);
    }

    private int helper(List<NestedInteger> nestedList, int res) {
        List<NestedInteger> nextList = new LinkedList<>();
        for (NestedInteger nest : nestedList) {
            if (nest.isInteger()) {
                res += nest.getInteger();
            } else {
                nextList.addAll(nest.getList());
            }
        }
        res += nextList.isEmpty() ? 0 : helper(nestedList, res);
        return res;
    }

    public int depthSumInverse2(List<NestedInteger> nestedList) {
        if (nestedList == null) return 0;
        int sum = 0;
        int res = 0;
        while (!nestedList.isEmpty()) {
            List<NestedInteger> nextList = new LinkedList<>();
            for (NestedInteger nest : nestedList) {
                if (nest.isInteger()) {
                    sum += nest.getInteger();
                } else {
                    nextList.addAll(nest.getList());
                }
            }
            res += sum;
            nestedList = nextList;
        }
        return res;
    }
}