find immediate neighbors (north, east, south, west) of any tile #n in a 9x9 grid in swift

main.swift
let row = n / 9
let col = n % 9
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main.swift
let north = (row > 0) ? (n - 9) : nil   // check if not in top row
let east = (col < 8) ? (n + 1) : nil    // check if not in rightmost column
let south = (row < 8) ? (n + 9) : nil   // check if not in bottom row
let west = (col > 0) ? (n - 1) : nil    // check if not in leftmost column
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main.swift
let row = n / 9
let col = n % 9

let north = (row > 0) ? (n - 9) : nil
let east = (col < 8) ? (n + 1) : nil
let south = (row < 8) ? (n + 9) : nil
let west = (col > 0) ? (n - 1) : nil

print("Neighbors of tile #\(n): north=\(north ?? -1), east=\(east ?? -1), south=\(south ?? -1), west=\(west ?? -1)")
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main.swift
Neighbors of tile #40: north=31, east=41, south=49, west=39
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