LeetCod 339.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.

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Example

Given the list [[1,1],2,[1,1]], return 10. (four 1's at depth 2, one 2 at depth 1, 4 * 1 * 2 + 1 * 2 * 1 = 10)
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 + 42 + 63 = 27)

解题思路：使用递归的方式将数据展开，然后分别于深度相乘

java

/** * // 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) {        // Write your code here        if (nestedList == null || nestedList.size() == 0) {            return 0;        }        return util(nestedList, 1);    }    private int util(List<NestedInteger> nestedList, int deepth) {        if (nestedList == null || nestedList.size() == 0) {            return 0;        }        int sum = 0;        for (int i = 0; i < nestedList.size(); i++) {            if (nestedList.get(i).isInteger()) {                sum += nestedList.get(i).getInteger() * deepth;            } else {                sum += util(nestedList.get(i).getList(), deepth + 1);            }        }        return sum;    }}