186. Reverse Words in a String II

func reverseWords(_ str: inout [Character]) {
        var i = 0
        while i < str.count {
            let last = i
            while i < str.count && str[i] != " "{
                i += 1
            }
            swap(&str, last, i - 1)
            i += 1
        }
        str.reverse()
    }

    func swap(_ str: inout [Character], _ s : Int, _ e : Int){
        var i = s
        var j = e
        while i < j {
            str.swapAt( i , j)
            i += 1
            j -= 1
        }
    }