compare number

func check(_ str1: String, _ str2 : String) ->Int {
    guard str1.count > 0 else { return str2.count}
    guard str2.count > 0 else { return str1.count}

    var p1 = 0
    var p2 = 0
    let l1 = Array(str1)
    let l2 = Array(str2)

    while p1 < l1.count && p2 < l2.count{
        let char1 = l1[p1]
        let char2 = l2[p2]
        if char1 == char2{
            p1 += 1
            p2 += 1
            continue
        }
        if !isDigit(char1)  || !isDigit(char2) { return char1 < char2 ? -1 : 1}     //not number
        let n1 = getNumber(&p1, l1)
        let n2 = getNumber(&p2, l2)
        if n1 != n2 {
            return n1 - n2
        }
        p1 += 1
        p2 += 1
    }
    if l1.count == l2.count {return 0}
    return p1 == l1.count ? -1 : 1
}

func isDigit(_ char : Character) -> Bool{
    return char >= "0" && char <= "9"
}
func getNumber(_ p : inout Int, _ arr : [Character]) -> Int{
    var n = 0
    while  p < arr.count && isDigit(arr[p]){
        n = n * 10 + Int(String(arr[p]))!
        p += 1
    }
    return n
}

let str1 = "a10b"
let str2 = "a2b"
print( check(str1, str2) )