How do you solve Flatten Deeply Nested Array on LeetCode?

Flatten Deeply Nested Array (LeetCode #2625) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Understanding recursion is crucial for solving nested structures.

What is the brute force solution for Flatten Deeply Nested Array?

The brute force approach for Flatten Deeply Nested Array is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves iterating through the array and checking if each element is an array. If it is, we will need to flatten it completely, regardless of the depth. This can lead to unnecessary operations and is not efficient. The optimal Optimal Solution approach improves this to O(n).

What are the interview tips for Flatten Deeply Nested Array?

Explain your thought process clearly while coding. Ask clarifying questions about edge cases. Test your solution with different inputs before finalizing.

What are common mistakes when solving Flatten Deeply Nested Array?

Failing to track the current depth correctly. Not handling base cases in recursion.

#2625

Flatten Deeply Nested Array

Medium

RecursionDepth-First Search

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

The optimal solution uses recursion to flatten the array while keeping track of the current depth. This allows us to only flatten elements when the current depth is less than n, making the solution efficient and straightforward.

⚙️

Algorithm

6 steps

1Step 1: Define a recursive function that takes the current array and depth.
2Step 2: Initialize an empty result array.
3Step 3: Iterate through each element in the array.
4Step 4: If the element is an integer, add it to the result array.
5Step 5: If the element is an array and the current depth is less than n, recursively flatten it and add to the result.
6Step 6: If the element is an array and the current depth is equal to or greater than n, add it as is to the result.

solution.py11 lines

1def flatten(arr, n, depth=0):
2    result = []
3    for element in arr:
4        if isinstance(element, list):
5            if depth < n:
6                result.extend(flatten(element, n, depth + 1))
7            else:
8                result.append(element)
9        else:
10            result.append(element)
11    return result

ℹ

Complexity note: The time complexity is O(n) because we visit each element in the array exactly once. The space complexity is O(n) due to the space used for the result array.

1Understanding recursion is crucial for solving nested structures.
2Keeping track of depth allows for controlled flattening.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.