LeetCode : 339. Nested List Weight Sum

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

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/**
 * // 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();
 * }
 */
class Solution {
    public int depthSum(List<NestedInteger> nestedList) {
        return getSum(nestedList, 1);
    }

    int getSum(List<NestedInteger> list, int depth) {
        if (list == null) return 0;

        int sum = 0;

        for (NestedInteger n : list) { // !!!
            if (n.isInteger()) sum += n.getInteger() * depth; // !!! getInteger() * depth
            else sum += getSum(n.getList(), depth + 1);
        }

        return sum;
    }
}

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