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Description
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.
Idea
let n=nestedList.length, d=max_depth
We could recursively explore into the nested list, keeping track of the recursion depth, and multiply the elements with the depth. We then sum up all the products of the multiplications.
We can analyze the time complexity with the recursion tree method. For more, see this post.
Complexity: Time , Space (recursion depth).
Python
# """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
from typing import Self
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) -> bool:
"""
@return True if this NestedInteger holds a single integer, rather than a nested list.
:rtype bool
"""
def add(self, elem):
"""
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) -> int | None:
"""
@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) -> list[Self] | None:
"""
@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:
"""780 ms, 7.28 mb"""
def depthSum(self, nil: list[NestedInteger]) -> int:
# nil: nested integer list, d: depth
def dfs(nil: list[NestedInteger], d):
res = 0
for i in nil:
if i.isInteger():
res += i.getInteger() * d
else:
res += dfs(i.getList(), d + 1)
return res
return dfs(nil, 1)
Java
// This is the interface that allows for creating nested lists.
// You should not implement it, or speculate about its implementation
interface NestedInteger {
// @return true if this NestedInteger holds a single integer,
// rather than a nested list.
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
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
List<NestedInteger> getList();
}
static class Solution {
int depthSum(List<NestedInteger> nil) {
return dfs(nil, 1);
}
int dfs(List<NestedInteger> nil, int d) {
int res = 0;
for (NestedInteger i : nil) {
if (i.isInteger()) res += i.getInteger() * d;
else res += dfs(i.getList(), d + 1);
}
return res;
}
}