NestedListWeightSum.java

package com.freetymekiyan.algorithms.level.easy;

import com.freetymekiyan.algorithms.utils.Utils.NestedInteger;

import java.util.List;

/**
 * Given a nested list of integers, return the sum of all integers in the list weighted by their depth.
 * <p>
 * Each element is either an integer, or a list -- whose elements may also be integers or other lists.
 * <p>
 * Example 1:
 * Given the list [[1,1],2,[1,1]], return 10. (four 1's at depth 2, one 2 at depth 1)
 * <p>
 * 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 + 4*2 + 6*3 = 27)
 * <p>
 * Company Tags: LinkedIn
 * Tags: Depth-first Search
 * Similar Problems: (M) Nested List Weight Sum II
 */
public class NestedListWeightSum {

    /**
     * Recursive.
     * sum = all integer's sum at this depth + all depthSum of other lists.
     */
    public int depthSum(List<NestedInteger> nestedList) {
        return depthSum(nestedList, 1);
    }

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