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LeetCode 339: Nested List Weight Sum Solution

Master LeetCode problem 339 (Nested List Weight Sum), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

339. Nested List Weight Sum

Medium
Depth-First SearchBreadth-First Search

Problem Explanation

Explanation

This problem asks us to find the sum of all nested list values weighted by their depth. We can achieve this by performing a depth-first search on the nested list structure. At each level of recursion, we update the sum by adding the values multiplied by their depth. If we encounter a nested list, we recursively call the function with the nested list and increment the depth.

Algorithm

  1. Initialize a variable sum to store the weighted sum.
  2. Define a recursive function calculateWeightSum that takes the nested list, current depth, and current sum as parameters.
  3. Iterate through each element in the nested list:
    • If the element is an integer, add the product of the integer and the current depth to the sum.
    • If the element is a nested list, recursively call calculateWeightSum with the nested list and increment the depth.
  4. Return the final sum.

Time Complexity: O(N), where N is the total number of integers in the nested list. Space Complexity: O(D), where D is the maximum depth of the nested list.

Java

Solution Code

public int depthSum(List<NestedInteger> nestedList) {
    return calculateWeightSum(nestedList, 1, 0);
}

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

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