How do you solve Spiral Matrix IV on LeetCode?

Spiral Matrix IV (LeetCode #2326) 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 how to navigate through a matrix using direction vectors is crucial for spiral traversal.

What is the brute force solution for Spiral Matrix IV?

The brute force approach for Spiral Matrix IV is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves filling the matrix in a spiral order by iterating through the linked list and placing each value into the matrix until we run out of values. Any remaining spaces in the matrix will be filled with -1. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Spiral Matrix IV?

Spiral Matrix IV uses the following concepts: Array, Linked List, Matrix, Simulation. The recommended patterns to study are: Matrix Traversal, Direction Vectors.

What are the interview tips for Spiral Matrix IV?

Always explain your thought process and how you plan to handle edge cases. Practice writing out the direction vectors and how they change with each step. Be prepared to discuss time and space complexities and justify your approach.

What are common mistakes when solving Spiral Matrix IV?

Failing to handle boundary conditions properly, which can lead to index errors. Not resetting the position correctly when changing directions.

#2326

Spiral Matrix IV

Medium

ArrayLinked ListMatrixSimulationMatrix TraversalDirection Vectors

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 a similar approach to the brute force but ensures that we efficiently navigate through the matrix using direction vectors. This reduces unnecessary checks and allows us to fill the matrix in a single pass.

⚙️

Algorithm

3 steps

1Step 1: Initialize the matrix with -1.
2Step 2: Use a direction vector to control movement in the matrix.
3Step 3: Iterate through the linked list, placing values into the matrix while checking bounds and direction changes.

solution.py23 lines

1class ListNode:
2    def __init__(self, val=0, next=None):
3        self.val = val
4        self.next = next
5
6def spiralMatrix(m, n, head):
7    matrix = [[-1] * n for _ in range(m)]
8    directions = [(0, 1), (1, 0), (0, -1), (-1, 0)]
9    x, y, d = 0, 0, 0
10    current = head
11    for _ in range(m * n):
12        if current:
13            matrix[x][y] = current.val
14            current = current.next
15        x += directions[d][0]
16        y += directions[d][1]
17        if x < 0 or x >= m or y < 0 or y >= n or matrix[x][y] != -1:
18            x -= directions[d][0]
19            y -= directions[d][1]
20            d = (d + 1) % 4
21            x += directions[d][0]
22            y += directions[d][1]
23    return matrix

ℹ

Complexity note: The time complexity is O(n) since we fill the matrix in a single pass through the linked list. The space complexity is O(n) due to the storage of the matrix.

1Understanding how to navigate through a matrix using direction vectors is crucial for spiral traversal.
2Filling the matrix with default values (like -1) helps in managing unfilled spaces effectively.

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