leetcode/java/339_Nested_List_Weight_Sum.java at master · jakehoare/leetcode · GitHub

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https://leetcode.com/problems/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.

For each item in list, if integer then multiply by depth and add to total, else recursively sum the list after

incrementing the depth.

Time - O(n)

Space - O(1)

/**

* // 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) {

return helper(nestedList, 1);

}

private int helper(List<NestedInteger> nestedList, int depth) {

int total = 0;

for (NestedInteger n : nestedList) {

if (n.isInteger())

total += n.getInteger() * depth;

else

total += helper(n.getList(), depth + 1);

}

return total;

}

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