NestedListWeightSum.java

import java.util.List;

/**
 * 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.
 * 
 * Example 1:
 * Given the list [[1,1],2,[1,1]], return 10. (four 1's at depth 2, one 2 at depth 1)
 */
public class NestedListWeightSum {

    public int depthSum(List<NestedInteger> nestedList) {
        return depthSum(nestedList, 1);
    }

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