339. Nested List Weight Sum

• Difficulty: Easy

• Topics: Depth-first Search

• Similar Questions:

  • Nested List Weight Sum II

  • Array Nesting

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Problem:

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.

Input: [[1,1],2,[1,1]]
Output: 10 
Explanation: Four 1's at depth 2, one 2 at depth 1.

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.

Solutions:

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * class NestedInteger {
 *   public:
 *     // Constructor initializes an empty nested list.
 *     NestedInteger();
 *
 *     // Constructor initializes a single integer.
 *     NestedInteger(int value);
 *
 *     // Return true if this NestedInteger holds a single integer, rather than a nested list.
 *     bool isInteger() const;
 *
 *     // Return the single integer that this NestedInteger holds, if it holds a single integer
 *     // The result is undefined if this NestedInteger holds a nested list
 *     int getInteger() const;
 *
 *     // Set this NestedInteger to hold a single integer.
 *     void setInteger(int value);
 *
 *     // Set this NestedInteger to hold a nested list and adds a nested integer to it.
 *     void add(const NestedInteger &ni);
 *
 *     // Return the nested list that this NestedInteger holds, if it holds a nested list
 *     // The result is undefined if this NestedInteger holds a single integer
 *     const vector<NestedInteger> &getList() const;
 * };
 */
class Solution {
public:
    int depthSum(vector<NestedInteger>& nestedList) {
        return helper(nestedList, 1);
    }
private:
    int helper(vector<NestedInteger>& nestedList, int depth) {
        int sum = 0;
        for (auto& nestedInt : nestedList) {
            if (nestedInt.isInteger()) {
                sum += depth * nestedInt.getInteger();
            } else {
                sum += helper(nestedInt.getList(), depth + 1);
            }
        }

        return sum;
    }

};