Nested List Weight Sum (easy)

update Jan 26,2018 11:12

LeetCode

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)

Basic Idea:

最简单的思路就是DFS，写一个helper function，传入一个depth，从1开始每层累加。

• Java Code:

    class Solution {
        public int depthSum(List<NestedInteger> nestedList) {
            // DFS
            return dfs(nestedList, 1);
        }
  
        private int dfs(List<NestedInteger> list, int depth) {
            int ret = 0;
            for (NestedInteger ni : list) {
                if (ni.isInteger()) {
                    ret += depth * ni.getInteger();
                } else {
                    ret += dfs(ni.getList(), depth + 1);
                }
            }
            return ret;
        }
    }