[Swift]LeetCode166. 分数到小数 | Fraction to Recurring Decimal

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➤微信公众号：山青咏芝（shanqingyongzhi）
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➤原文地址：https://www.cnblogs.com/strengthen/p/10127520.html 
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Given two integers representing the numerator and denominator of a fraction, return the fraction in string format.

If the fractional part is repeating, enclose the repeating part in parentheses.

Example 1:

Input: numerator = 1, denominator = 2
Output: "0.5"

Example 2:

Input: numerator = 2, denominator = 1
Output: "2"

Example 3:

Input: numerator = 2, denominator = 3
Output: "0.(6)"

---

给定两个整数，分别表示分数的分子 numerator 和分母 denominator，以字符串形式返回小数。

如果小数部分为循环小数，则将循环的部分括在括号内。

示例 1:

输入: numerator = 1, denominator = 2
输出: "0.5"

示例 2:

输入: numerator = 2, denominator = 1
输出: "2"

示例 3:

输入: numerator = 2, denominator = 3
输出: "0.(6)"

---

8ms

class Solution {
    func fractionToDecimal(_ numerator: Int, _ denominator: Int) -> String {
        let s1 = numerator > 0 ? 1 : -1
        let s2 = denominator > 0 ? 1 : -1
        let numerator = abs(numerator)
        let denominator = abs(denominator)
        let num = numerator / denominator
        var remain = numerator % denominator 
        var remains = [Int : Int]()
        var res = ""
        if s1*s2 < 0 && (num > 0 || remain > 0) {
            res += "-"
        }
        res += "(num)"
        if remain > 0 {
            res += "."
        }
        var frac = ""
        var pos = 0
        while remain > 0 {
            if let pos = remains[remain] {
                frac.insert("(", at: frac.index(frac.startIndex, offsetBy: pos))
                frac += ")"
                return res+frac
            }
            remains[remain] = pos
            frac += String(remain*10 / denominator)
            remain = remain*10 % denominator
            pos += 1
        }
        return res+frac
    }
}

---

12ms

class Solution {
    func fractionToDecimal(_ numerator: Int, _ denominator: Int) -> String {
        
        if denominator == 0 { return "NaN" }
        
        //Big bad voodoo magic.
        var numerator = numerator
        var denominator = denominator
        
        //Note, for bools "!=" behaves the same as "^" which is not allowed.
        var negative = (numerator < 0) != (denominator < 0)
        
        numerator = abs(numerator)
        denominator = abs(denominator)
        
        var result = String(numerator / denominator)
        var remainder = (numerator % denominator) * 10
        
        if remainder == 0 {
            if negative == true && numerator != 0 {
                return String("-") + result
            } else {
                return result
            }
        }
        
        result += "."
        
        //See if we find repeating digits...
        //At the point where our long division keeps
        //dividing into the same NO, we loop 4evz
        var repeatMap = [Int:Int]()
        
        while remainder != 0 {
            
            //We got a repeater? Or nah?
            if let repeatIndex = repeatMap[remainder] {
                result.insert("(", at: result.index(result.startIndex, offsetBy: repeatIndex))
                result += ")"
                break
            }
            
            result += String(remainder / denominator)
            
            //Set our repeater..
            repeatMap[remainder] = result.count - 1
            
            //Perform one more step of long division
            remainder = (remainder % denominator) * 10 
        }

        if negative == true {
            return String("-") + result
        }
        return result
    }
}

---

12ms

class Solution {
    func fractionToDecimal(_ numerator: Int, _ denominator: Int) -> String {
        
        if numerator  == 0 {
            return "0"
        }
        
        var res = ""
        
        if ((numerator < 0) && (denominator >= 0)) || ((numerator >= 0) && (denominator < 0)) {
            res += "-"
        }
        
        let absNum = abs(numerator)
        let absDen = abs(denominator)
        
        res += String(absNum/absDen)
        
        var remander = absNum % absDen
        
        if remander == 0 {
            return res
        }
        
        res += "."
        
        var remanders = [Int : Int]()
        
        var pos = res.count
        
        var add = 0
        var hasRecycyle = false
        
        while remander != 0 && !hasRecycyle {
            if remanders.keys.contains(remander) {
                add = remanders[remander]!
                hasRecycyle = true
                continue
            }
            
            remanders[remander] = pos
            pos += 1
            res += String(10 * remander / absDen)
            remander = (10 * remander) % absDen
        }
        
        if hasRecycyle {
            res.insert("(", at: res.index(res.startIndex, offsetBy: add))
            res += ")"
        }
        
        
        return res
    }
}

---

16ms

class Solution {
    func fractionToDecimal(_ numerator: Int, _ denominator: Int) -> String {
        var s1:Int = numerator >= 0 ? 1 : -1
        var s2:Int = denominator >= 0 ? 1 : -1
        var num:Int = abs(numerator )
        var den:Int = abs(denominator )
        var out:Int = num / den
        var rem:Int = num % den
        var m:[Int: Int] = [Int: Int]()
        var res:String = String(out)
        if s1 * s2 == -1 && (out > 0 || rem > 0)
        {
            res = "-" + res
        }
        if rem == 0 {return res}
        res += "."
        var s:String = ""
        var pos:Int = 0
        while(rem != 0)
        {
            if m[rem] != nil
            {
                var index = s.index(s.startIndex, offsetBy: m[rem]!)
                s.insert("(", at:index )
                s += ")"
                return res + s
            }
            m[rem] = pos
            s += String((rem * 10) / den)
            rem = (rem * 10) % den
            pos += 1
        }
        return res + s
    }
}

---

20ms

class Solution {
    func fractionToDecimal(_ numerator: Int, _ denominator: Int) -> String {
        
        if numerator % denominator == 0 {
            return String(numerator/denominator)
        }
        
        let n = abs(numerator);
        let d = abs(denominator);
        
        var sign = ""
        
        if numerator > 0 && denominator < 0 || numerator < 0 && denominator > 0{
            sign = "-"
        }
        
        var i = n
        while i > d {
            i = i/d
        }
        
        var dic = Dictionary<Int, Int>()
        
        var res = n % d;
        var s = String()
        
        var count = 0
        
        repeat {
            dic[res] = count
            res = res * 10;
            s.append(String(abs(res/d)))
            res = res % d
            count = count + 1
        } while (res != 0 && dic[res] == nil)
        
        if res == 0 {
            return sign + String(n/d) + "." + s;
        }
        let idx = s.index(s.startIndex, offsetBy: dic[res]!)
        return sign + String(n/d) + "." + s.substring(to: idx) + "(" + s.substring(from: idx) + ")"
    }
}

---

20ms

class Solution {
    func fractionToDecimal(_ numerator: Int, _ denominator: Int) -> String {
        let r = numerator % denominator
        let k = numerator / denominator
        if r == 0 {
            return "(k)"
        }
        
        let tail = helper(abs(r), abs(denominator))
        var ret = "(abs(k)).(tail)"
        if numerator * denominator < 0 {
            ret = "-" + ret
        }
        return ret
    }
    
    
    func helper(_ n: Int, _ m: Int) -> String {
        var ret = ""
        var map = [Int: Int]()
        var x = n
        while x != 0 {
            if let i = map[x] {
                ret = ret.prefix(i) + "(" + ret.suffix(ret.count - i) + ")"
                return ret
            }
            let y = x * 10
            let k = y / m
            map[x] = ret.count
            ret += "(k)"
            x = y % m
        }
        return ret
    }
}

---

36ms

class Solution {
    func fractionToDecimal(_ numerator: Int, _ denominator: Int) -> String {
         if denominator == 0 {
            return ""
        }
        
        if numerator == 0 {
            return "0"
        }
        
        //取绝对值
        var num1 = numerator > 0 ? numerator : -numerator
        let num2 = denominator > 0 ? denominator : -denominator
        //取方向
        var  result = (numerator > 0 && denominator < 0) || (numerator < 0 && denominator > 0) ? "-" : ""
        
        //整数部分
        result += String(num1/num2)
        num1 = num1 % num2
        if num1 == 0 {
            return result
        }else {
            result += "."
        }
        
        //小数部分
        var dic = [Int:Int]()
        
        while num1 != 0 {
            if dic.keys.contains(num1) {
                let index = result.index(result.startIndex, offsetBy: dic[num1]!)
                result.insert("(", at: index)
                result += ")"
                break
            }
            dic[num1] = result.count
            num1 *= 10
            result += String(num1/num2)
            num1 %= num2
        }
        return result
    }
}

---

56ms

class Solution {
    func fractionToDecimal(_ numerator: Int, _ denominator: Int) -> String {
        if numerator == 0 { return "0" }
        let sign = (numerator > 0 ? 1 : -1) ^ (denominator > 0 ? 1 : -1) == 0 ? "" : "-"
        var result = sign
        var a = abs(numerator)
        let b = abs(denominator)
        result += "(a/b)"
        a = a % b
        if a != 0 {
            result += "."
        } else {
            return result
        }
        var decimal = ""
        var array = [a]
        while true {
            a = a * 10
            decimal += "(a/b)"
            a = a % b
            if a == 0 {
                result += decimal
                return result
            }
            if let index = array.index(of: a) {
                var temp = [Character](decimal)
                temp.insert("(", at: index)
                temp.append(")")
                result += String(temp)
                return result
            } else {
                array.append(a)
            }
        }
    }
}