339. Nested List Weight Sum.java

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