Introduction

In this blog post, we will explore how to solve the LeetCode problem "892" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

You are given an n x n grid where you have placed some 1 x 1 x 1 cubes. Each value v = grid[i][j] represents a tower of v cubes placed on top of cell (i, j). After placing these cubes, you have decided to glue any directly adjacent cubes to each other, forming several irregular 3D shapes. Return the total surface area of the resulting shapes. Note: The bottom face of each shape counts toward its surface area. Example 1: Input: grid = [[1,2],[3,4]] Output: 34 Example 2: Input: grid = [[1,1,1],[1,0,1],[1,1,1]] Output: 32 Example 3: Input: grid = [[2,2,2],[2,1,2],[2,2,2]] Output: 46 Constraints: n == grid.length == grid[i].length 1 <= n <= 50 0 <= grid[i][j] <= 50

Explanation

Here's a solution to calculate the surface area of the 3D shapes formed by the cubes:

• Iterate through the grid: For each cell (i, j), calculate the surface area contributed by the tower of cubes at that cell.
• Base Surface Area: Each cell contributes 2 to the total surface area (top and bottom faces) if grid[i][j] > 0.

• Lateral Surface Area: For each cell, calculate the lateral surface area by considering adjacent cells (up, down, left, right). If an adjacent cell has fewer cubes, the difference contributes to the surface area.

• Runtime Complexity: O(n^2), Storage Complexity: O(1)

Code

    def surfaceArea(grid):
    """
    Calculates the surface area of 3D shapes formed by cubes in a grid.

    Args:
        grid: A list of lists representing the grid of cube towers.

    Returns:
        The total surface area of the 3D shapes.
    """

    n = len(grid)
    area = 0

    for i in range(n):
        for j in range(n):
            if grid[i][j] > 0:
                area += 2  # Top and bottom faces

                # Calculate lateral surface area
                for dx, dy in [(0, 1), (0, -1), (1, 0), (-1, 0)]:
                    x, y = i + dx, j + dy
                    neighbor_height = 0
                    if 0 <= x < n and 0 <= y < n:
                        neighbor_height = grid[x][y]
                    area += max(0, grid[i][j] - neighbor_height)

    return area