# Question

Formatted question description: https://leetcode.ca/all/339.html

You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists.

The depth of an integer is the number of lists that it is inside of. For example, the nested list [1,[2,2],[[3],2],1] has each integer's value set to its depth.

Return the sum of each integer in nestedList multiplied by its depth.

Example 1:

Input: nestedList = [[1,1],2,[1,1]]
Output: 10
Explanation: Four 1's at depth 2, one 2 at depth 1. 1*2 + 1*2 + 2*1 + 1*2 + 1*2 = 10.

Example 2:

Input: nestedList = [1,[4,[6]]]
Output: 27
Explanation: One 1 at depth 1, one 4 at depth 2, and one 6 at depth 3. 1*1 + 4*2 + 6*3 = 27.

Example 3:

Input: nestedList = [0]
Output: 0

Constraints:

• 1 <= nestedList.length <= 50
• The values of the integers in the nested list is in the range [-100, 100].
• The maximum depth of any integer is less than or equal to 50.

# Algorithm

Traverse the given nested linked list array, for each nested linked list object, call the dfs function, assign a depth value of 1, and add up and return. In the dfs function, first determine whether it is an integer,

• If yes, it returns the current depth multiplied by an integer
• If not, then we traverse the nested array again, call the recursive function for each nested linked list, and add up the return value to return

# Code

• import java.util.List;

public class Nested_List_Weight_Sum {
/**
* // 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_dfs {
public int depthSum(List<NestedInteger> nestedList) {
if (nestedList == null || nestedList.size() == 0) {
return 0;
}

return depthSumHelper(nestedList, 1);
}

private int depthSumHelper(List<NestedInteger> list, int depth) {
if (list.isEmpty()) {
return 0;
}

int sum = 0;

for (NestedInteger curr: list){
// for each in list, perform a dfs
if (curr.isInteger()) {
sum += curr.getInteger() * depth;
} else {
sum += depthSumHelper(curr.getList(), depth + 1);
}
}

return sum;
}
}

public class Solution_stack {

/*
用一个stack来实现。
遍历list，将当前元素和深度加入stack中。
依次取出栈顶元素，
若取出元素为数，则将其乘以其深度并加入sum，
若取出元素是list，则将该list中元素依次加入stack中，同时这些元素的深度比之前取出元素深度＋1
*/
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 current = stack.pop();
if (current.nestedInteger.isInteger()) {
sum += current.depth * current.nestedInteger.getInteger();
} else {
List<NestedInteger> list = current.nestedInteger.getList();
for (int i = 0; i < list.size(); i++) {
stack.push(new Node(current.depth + 1, list.get(i)));
}
}
}

return sum;
}
}

// This is the interface that allows for creating nested lists.
// You should not implement it, or speculate about its implementation
private 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();
}
}

############

/**
* // 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.
*
*     // @return the nested list that this NestedInteger holds, if it holds a nested list
*     // Return empty list if this NestedInteger holds a single integer
*     public List<NestedInteger> getList();
* }
*/
class Solution {
public int depthSum(List<NestedInteger> nestedList) {
return dfs(nestedList, 1);
}

private int dfs(List<NestedInteger> nestedList, int depth) {
int depthSum = 0;
for (NestedInteger item : nestedList) {
if (item.isInteger()) {
depthSum += item.getInteger() * depth;
} else {
depthSum += dfs(item.getList(), depth + 1);
}
}
return depthSum;
}
}

• // OJ: https://leetcode.com/problems/nested-list-weight-sum/
// Time: O(N)
// Space: O(D) where D is the max depth of the list.
class Solution {
private:
int depthSum(vector<NestedInteger>& nestedList, int depth) {
int sum = 0;
for (auto &i : nestedList) {
if (i.isInteger()) sum += i.getInteger() * depth;
else sum += depthSum(i.getList(), depth + 1);
}
return sum;
}
public:
int depthSum(vector<NestedInteger>& nestedList) {
return depthSum(nestedList, 1);
}
};

• # """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
# class NestedInteger:
#    def __init__(self, value=None):
#        """
#        If value is not specified, initializes an empty list.
#        Otherwise initializes a single integer equal to value.
#        """
#
#    def isInteger(self):
#        """
#        @return True if this NestedInteger holds a single integer, rather than a nested list.
#        :rtype bool
#        """
#
#        """
#        Set this NestedInteger to hold a nested list and adds a nested integer elem to it.
#        :rtype void
#        """
#
#    def setInteger(self, value):
#        """
#        Set this NestedInteger to hold a single integer equal to value.
#        :rtype void
#        """
#
#    def getInteger(self):
#        """
#        @return the single integer that this NestedInteger holds, if it holds a single integer
#        Return None if this NestedInteger holds a nested list
#        :rtype int
#        """
#
#    def getList(self):
#        """
#        @return the nested list that this NestedInteger holds, if it holds a nested list
#        Return None if this NestedInteger holds a single integer
#        :rtype List[NestedInteger]
#        """
class Solution:
def depthSum(self, nestedList: List[NestedInteger]) -> int:
def dfs(nestedList, depth):
depth_sum = 0
for item in nestedList:
if item.isInteger():
depth_sum += item.getInteger() * depth
else:
depth_sum += dfs(item.getList(), depth + 1)
return depth_sum

return dfs(nestedList, 1)

class Solution: # iterative
def depthSum(self, nestedList):
stack = []
for nestedInteger in nestedList:
stack.append((1, nestedInteger))

ans = 0
while stack:
depth, current = stack.pop()
if current.isInteger():
ans += depth * current.getInteger()
else:
lst = current.getList()
for nestedInteger in lst:
stack.append((depth+1, nestedInteger))

return ans

############

# """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
# class NestedInteger(object):
#    def isInteger(self):
#        """
#        @return True if this NestedInteger holds a single integer, rather than a nested list.
#        :rtype bool
#        """
#
#    def getInteger(self):
#        """
#        @return the single integer that this NestedInteger holds, if it holds a single integer
#        Return None if this NestedInteger holds a nested list
#        :rtype int
#        """
#
#    def getList(self):
#        """
#        @return the nested list that this NestedInteger holds, if it holds a nested list
#        Return None if this NestedInteger holds a single integer
#        :rtype List[NestedInteger]
#        """

class Solution(object):
def depthSum(self, nestedList):
"""
:type nestedList: List[NestedInteger]
:rtype: int
"""

def helper(root, depth):
res = 0
for nested in root:
if nested.isInteger():
res += depth * nested.getInteger()
else:
res += helper(nested.getList(), depth + 1)
return res

return helper(nestedList, 1)

• /**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* function NestedInteger() {
*
*     Return true if this NestedInteger holds a single integer, rather than a nested list.
*     @return {boolean}
*     this.isInteger = function() {
*         ...
*     };
*
*     Return the single integer that this NestedInteger holds, if it holds a single integer
*     Return null if this NestedInteger holds a nested list
*     @return {integer}
*     this.getInteger = function() {
*         ...
*     };
*
*     Set this NestedInteger to hold a single integer equal to value.
*     @return {void}
*     this.setInteger = function(value) {
*         ...
*     };
*
*     Set this NestedInteger to hold a nested list and adds a nested integer elem to it.
*     @return {void}
*         ...
*     };
*
*     Return the nested list that this NestedInteger holds, if it holds a nested list
*     Return null if this NestedInteger holds a single integer
*     @return {NestedInteger[]}
*     this.getList = function() {
*         ...
*     };
* };
*/
/**
* @param {NestedInteger[]} nestedList
* @return {number}
*/
var depthSum = function (nestedList) {
const dfs = (nestedList, depth) => {
let depthSum = 0;
for (const item of nestedList) {
if (item.isInteger()) {
depthSum += item.getInteger() * depth;
} else {
depthSum += dfs(item.getList(), depth + 1);
}
}
return depthSum;
};
return dfs(nestedList, 1);
};