Practice/Google/Leetcode 463. Island Perimeter

Leetcode 463. Island Perimeter

CodingMust

Problem

You are given a 2D grid map where cells contain either 0 (representing water) or 1 (representing land). The grid contains exactly one island, which is a connected group of land cells joined horizontally or vertically (not diagonally).

Your task is to calculate the total perimeter of this island. The perimeter is defined as the total number of edges of land cells that border either water cells or the edge of the grid.

Requirements

1. Count every side of a land cell that touches water or a grid boundary
2. The grid contains exactly one island with no lakes (isolated water cells completely surrounded by land don't exist)
3. All land cells in the island are connected horizontally or vertically
4. Return the total count of exposed edges

Constraints

• 1 ≤ grid.length, grid[0].length ≤ 100
• grid[i][j] is either 0 or 1
• The grid contains exactly one island
• Land cells connect only horizontally or vertically (not diagonally)

Examples

Example 1:

Input: grid = [[0,1,0,0], [1,1,1,0], [0,1,0,0], [1,1,0,0]] Output: 16 Explanation: The island spans multiple cells forming an irregular shape. Count each edge that faces water or the grid boundary.

Example 2:

Input: grid = [[1]] Output: 4 Explanation: A single cell island has all four sides exposed.

Example 3:

Input: grid = [[1,1], [1,1]] Output: 8 Explanation: The 2×2 square island has 8 outer edges (each of the 4 cells contributes 2 exposed sides).