NestedListWeightSum339.java

/**
 * 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:
 * Input: [[1,1],2,[1,1]]
 * Output: 10 
 * Explanation: Four 1's at depth 2, one 2 at depth 1.
 * 
 * Example 2:
 * Input: [1,[4,[6]]]
 * Output: 27 
 * Explanation: One 1 at depth 1, one 4 at depth 2, and one 6 at depth 3;
 * 1 + 4*2 + 6*3 = 27.
 */

/**
 * // 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();
 * }
 */

public class NestedListWeightSum339 {
    public int depthSum(List<NestedInteger> nestedList) {
        return depthSum(nestedList, 1);
    }

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

}