백준 쉬운최단거리 14940번

import Foundation

let input = readLine()!.split(separator: " ").map{ Int(String($0))! }
let n = input[0], m = input[1]
var matrix: [[Int]] = []
var answer: [[Int]] = []
var visited: [[Bool]] = Array(repeating: Array(repeating: false, count: m), count: n)

(0..<n).forEach { _ in
    let row = readLine()!.split(separator: " ").map{ Int(String($0))! }
    matrix.append(row)
}

var start: (y:Int, x: Int) = (y: 0, x: 0)

for (i, row) in matrix.enumerated() {
    var aRow: [Int] = []
    for (j, d) in row.enumerated() {
        
        if d == 0 {
            aRow.append(0)
        } else if d == 1 {
            aRow.append(-1)
        } else {
            start = (y: i, x: j)
            aRow.append(0)
        }
        
    }
    answer.append(aRow)
}

func bfs(sy: Int, sx: Int) {
    var queue: [(y: Int, x: Int)] = [(sy,sx)]
    let dy = [0, 0, 1, -1]
    let dx = [1, -1, 0, 0]
    
    while !queue.isEmpty {
        let (y,x) = queue.removeFirst()
        
        (0..<4).forEach { i in
            let ny = dy[i] + y
            let nx = dx[i] + x
            
            if ny >= 0 && ny < n && nx >= 0 && nx < m && !visited[ny][nx] {
                if matrix[ny][nx] == 0 {
                    answer[ny][nx] = 0
                    return
                }
                answer[ny][nx] = answer[y][x] + 1
                
                visited[ny][nx] = true
                queue.append((ny, nx))
            }
        }
    }
}

visited[start.y][start.x] = true
bfs(sy: start.y, sx: start.x)

answer.forEach {
    print($0.map{ String($0) }.joined(separator: " "))
}