LeetCode 2649: Nested Array Generator Solution

Master LeetCode problem 2649 (Nested Array Generator), 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.

2649. Nested Array Generator

Medium

Problem Explanation

Explanation:

To solve this problem without creating a new flattened version of the array, we can implement a generator function that performs an inorder traversal on the multi-dimensional array. We can use a recursive approach to handle nested arrays.

Define a generator function inorderTraversal that takes the multi-dimensional array as input.
Iterate over the array elements, and for each element:
- If the element is an integer, yield the integer.
- If the element is an array, recursively call inorderTraversal on the sub-array.
The generator will yield integers in the order they are encountered during the inorder traversal of the multi-dimensional array.

Time Complexity: The time complexity of this approach is O(N), where N is the total number of integers in the multi-dimensional array.

Space Complexity: The space complexity is also O(N) due to the recursion stack.

Solution Code

import java.util.Iterator;
import java.util.List;

public class NestedArrayGenerator {
    public static Iterator<Integer> inorderTraversal(List<Object> arr) {
        return new Iterator<Integer>() {
            private Iterator<Object> iterator = arr.iterator();
            private Iterator<Integer> currentIterator = null;

            @Override
            public boolean hasNext() {
                while ((currentIterator == null || !currentIterator.hasNext()) && iterator.hasNext()) {
                    Object obj = iterator.next();
                    if (obj instanceof Integer) {
                        currentIterator = List.of((Integer) obj).iterator();
                    } else if (obj instanceof List) {
                        currentIterator = inorderTraversal((List<Object>) obj);
                    }
                }
                return currentIterator != null && currentIterator.hasNext();
            }

            @Override
            public Integer next() {
                return currentIterator.next();
            }
        };
    }
}

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