IslandPerimeter.swift

/**
 * Question Link: https://leetcode.com/problems/island-perimeter/
 * Primary idea: Go through the matrix and check right and down neighbors.
 * Time Complexity: O(nm), Space Complexity: O(1)
 *
 */

class IslandPerimeter {
    func islandPerimeter(_ grid: [[Int]]) -> Int {
        var islands = 0, neighbors = 0
        
        for i in 0 ..< grid.count {
            for j in 0 ..< grid[0].count {
                if grid[i][j] == 1 {
                    islands += 1
                    if i < grid.count - 1 && grid[i + 1][j] == 1 {
                        neighbors += 1
                    }
                    if (j < grid[0].count - 1 && grid[i][j + 1] == 1) {
                        neighbors += 1
                    }
                }
            }
        }
        
        return islands * 4 - neighbors * 2
    }
}