[Swift][DFS] 백준 2580번 (스도쿠)

import Foundation
var arr = [[Int]]()
var col = Array(repeating: Array(repeating: false, count: 10), count: 9)
var row = Array(repeating: Array(repeating: false, count: 10), count: 9)
var square = Array(repeating: Array(repeating: false, count: 10), count: 9)
for i in 0..<9{
    arr.append(readLine()!.split(separator: " ").map{Int(String($0))!})
    for j in 0..<9{
        if arr[i][j] != 0{
            col[i][arr[i][j]] = true
            row[j][arr[i][j]] = true
            square[(i / 3) * 3 + (j / 3)][arr[i][j]] = true
        }
    }
}


func dfs(_ depth: Int){
    let x = depth / 9
    let y = depth % 9
    if depth == 81{

            for i in 0..<9{
                for j in 0..<9{
                    print(arr[i][j], terminator: " ")
                }
                print()
            }
        exit(0)
    }

    if arr[x][y] == 0{
        for i in 1..<10{
            if !col[x][i] && !row[y][i] && !square[(x / 3) * 3 + (y / 3)][i]{
                col[x][i] = true
                row[y][i] = true
                square[(x / 3) * 3 + (y / 3)][i] = true
                arr[x][y] = i
                dfs(depth + 1)
                col[x][i] = false
                row[y][i] = false
                square[(x / 3) * 3 + (y / 3)][i] = false
                arr[x][y] = 0
            }
        }
    }else{
        dfs(depth + 1)
    }

}
dfs(0)