https://leetcode.com/problems/nested-list-weight-sum/description/

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 + 42 + 63 = 27)

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * public interface NestedInteger {
 *     // Constructor initializes an empty nested list.
 *     public NestedInteger();
 *
 *     // Constructor initializes a single integer.
 *     public NestedInteger(int value);
 *
 *     // @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();
 *
 *     // Set this NestedInteger to hold a single integer.
 *     public void setInteger(int value);
 *
 *     // Set this NestedInteger to hold a nested list and adds a nested integer to it.
 *     public void add(NestedInteger ni);
 *
 *     // @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();
 * }
 */

my DFS solution

    public int depthSum(List<NestedInteger> nestedList) {
        return depthSumHelper(nestedList, 1);
    }
    
    private int depthSumHelper(List<NestedInteger> nestedList, int level) {
        int sum = 0;
        for (NestedInteger ni: nestedList) {
            if (ni.isInteger()) {
                sum += ni.getInteger() * level;
            } else {
                sum += depthSumHelper(ni.getList(), level + 1);
            }
        }
        return sum;
    }

BFS solution

from: https://www.jiuzhang.com/solution/nested-list-weight-sum/

public int depthSum(List<NestedInteger> nestedList) {
        // Write your code here
        if (nestedList == null || nestedList.size() == 0) {
            return 0;
        }
        int sum = 0;
        Queue<NestedInteger> queue = new LinkedList<NestedInteger>();
        for (NestedInteger nestedInt : nestedList) {
            queue.offer(nestedInt);
        }

        int depth = 0;
        while (!queue.isEmpty()) {
            int size = queue.size();
            depth++;
            for (int i = 0; i < size; i++) {
                NestedInteger nestedInt = queue.poll();
                if (nestedInt.isInteger()) {
                    sum += nestedInt.getInteger() * depth;
                } else {
                    for (NestedInteger innerInt : nestedInt.getList()) {
                        queue.offer(innerInt);
                    }
                }
            }
        }
        return sum;
    }

DFS recursion

from: https://zhengyang2015.gitbooks.io/lintcode/nested_list_weight_sum_551.html

class Node{
    int depth;
    NestedInteger nestedInteger;
    public Node(int depth, NestedInteger nestedInteger){
        this.depth = depth;
        this.nestedInteger = nestedInteger;
    }
}

public int depthSum(List<NestedInteger> nestedList) {
        Stack<Node> stack = new Stack<Node>();
        for(int i = 0; i < nestedList.size(); i++){
            stack.push(new Node(1, nestedList.get(i)));
        }

        int sum = 0;
        while(!stack.isEmpty()){
            Node curt = stack.pop();
            if(curt.nestedInteger.isInteger()){
                sum += curt.depth * curt.nestedInteger.getInteger();
            }else{
                List<NestedInteger> list = curt.nestedInteger.getList();
                for(int i = 0; i < list.size(); i++){
                    stack.push(new Node(curt.depth + 1, list.get(i)));
                }
            }
        }

        return sum;
    }