[Math] Add a solution to Fraction to Recurring Decimal

Math/FractionToRecurringDecimal.swift

@@ -0,0 +1,46 @@
+/**
+ * Question Link: https://leetcode.com/problems/fraction-to-recurring-decimal/
+ * Primary idea: Get quotient and remainder, if remainder exists, then it is repeating.
+ * Time Complexity: O(logn), Space Complexity: O(n)
+ *
+ */
+
+class FractionToRecurringDecimal {
+    func fractionToDecimal(_ numerator: Int, _ denominator: Int) -> String { 
+        guard numerator != 0 else {
+            return "0"
+        }
+        guard denominator != 0 else {
+            fatalError("Invalid Denominator")
+        }
+
+        var isPositive = (numerator < 0) == (denominator < 0), numerator = abs(numerator), res = "", numToIndex = [Int: Int](), hasDot = false
+        let denominator = abs(denominator)
+
+        while numerator != 0 {
+
+            let (q, r) = numerator.quotientAndRemainder(dividingBy: denominator)
+
+            if let numIndex = numToIndex[numerator]{
+                res.insert("(", at: res.index(res.startIndex, offsetBy: numIndex))
+                res.append(")")
+                break
+            } else {
+                res += "\(q)"
+
+                if !hasDot && r != 0 {
+                    res.append(".")
+                    hasDot = true
+                } else {
+                    // update numToIndex
+                    numToIndex[numerator] = res.count - 1
+                }
+
+                // update reminder
+                numerator = r * 10
+            }
+        }
+
+        return isPositive ? res : "-" + res
+    }
+}

README.md

@@ -305,7 +305,7 @@
 [Super Ugly Number](https://leetcode.com/problems/super-ugly-number/)| [Swift](./Math/SuperUglyNumber.swift)| Medium| O(n^2)| O(n)|
 [Count Primes](https://leetcode.com/problems/count-primes/)| [Swift](./Math/CountPrimes.swift)| Easy| O(n)| O(n)|
 [String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/)| [Swift](./Math/Atoi.swift)| Easy| O(n)| O(1)|
-[Fraction to Recurring Decimal](https://leetcode.com/problems/fraction-to-recurring-decimal/)| [Swift](FractionToRecurringDecimal.swift) | Medium| O(logn)| O(n)|
+[Fraction to Recurring Decimal](https://leetcode.com/problems/fraction-to-recurring-decimal/)| [Swift](./Math/FractionToRecurringDecimal.swift) | Medium| O(logn)| O(n)|
 [Pow(x, n)](https://leetcode.com/problems/isomorphic-strings/)| [Swift](./Math/Pow.swift)| Medium| O(logn)| O(1)|
 [Power of Two](https://leetcode.com/problems/power-of-two/)| [Swift](./Math/PowerTwo.swift)| Easy| O(1)| O(1)|
 [Power of Three](https://leetcode.com/problems/power-of-three/)| [Swift](./Math/PowerThree.swift)| Easy| O(1)| O(1)|
@@ -705,7 +705,7 @@
 | [Swift](./Array/MajorityElement.swift)  |	169	|	[Majority Element](https://oj.leetcode.com/problems/majority-element/)	| Easy	|
 |		|	168	|	[Excel Sheet Column Title](https://oj.leetcode.com/problems/excel-sheet-column-title/)	| Easy	|
 |		|	167	|	[Two Sum II - Input array is sorted](https://oj.leetcode.com/problems/two-sum-ii-input-array-is-sorted/) ♥	| Medium	|
-|		|	166	|	[Fraction to Recurring Decimal](https://oj.leetcode.com/problems/fraction-to-recurring-decimal/)	| Medium	|
+|	[Swift](./Math/FractionToRecurringDecimal.swift)	|	166	|	[Fraction to Recurring Decimal](https://oj.leetcode.com/problems/fraction-to-recurring-decimal/)	| Medium	|
 |		|	165	|	[Compare Version Numbers](https://oj.leetcode.com/problems/compare-version-numbers/)	| Easy	|
 |		|	164	|	[Maximum Gap](https://oj.leetcode.com/problems/maximum-gap/)	| Hard	|
 |	[Swift](./Array/MissingRanges.swift)	|	163	|	[Missing Ranges](https://oj.leetcode.com/problems/missing-ranges/) ♥	| Medium	|