solves fraction to decimal in leetcode

Author: anishLearnsToCode

README.md

@@ -145,7 +145,7 @@
 | 161  | 🔒 [One Edit Distance](https://leetcode.com/problems/one-edit-distance)                                                                                   |                                                                                                                                                                                      |                                                                                                                                   |
 | 162  | [Find Peak Element](https://leetcode.com/problems/find-peak-element)                                                                                      |                                                                 [![Java](assets/java.png)](src/FindPeakElement.java)                                                                 |                                                                                                                                   |
 | 165  | [Compare Version Numbers](https://leetcode.com/problems/compare-version-numbers)                                                                          |                                                              [![Java](assets/java.png)](src/CompareVersionNumbers.java)                                                              |                                                                                                                                   |
-| 166  | [Fraction to Recurring Decimal](https://leetcode.com/problems/fraction-to-recurring-decimal)                                                              |                                                                                                                                                                                      |                                                                                                                                   |
+| 166  | [Fraction to Recurring Decimal](https://leetcode.com/problems/fraction-to-recurring-decimal)                                                              |                                                           [![Java](assets/java.png)](src/FractionToRecurringDecimal.java)                                                            |                                                                                                                                   |
 | 167  | [Two Sum II - Input Array is Sorted](https://leetcode.com/problems/two-sum-ii-input-array-is-sorted)                                                      |                                 [![Java](assets/java.png)](src/TwoSumIIInputArrayIsSorted.java) [![Python](assets/python.png)](python/two_sum_ii.py)                                 |                                                                                                                                   |
 | 168  | [Excel Sheet Column Title](https://leetcode.com/problems/excel-sheet-column-title)                                                                        |                            [![Java](assets/java.png)](src/ExcelSheetColumnTitle.java) [![Python](assets/python.png)](python/excel_sheet_column_title.py)                             |                                                                                                                                   |
 | 169  | [Majority Element](https://leetcode.com/problems/majority-element)                                                                                        |                                   [![Java](assets/java.png)](src/MajorityElement.java) [![Python](assets/python.png)](python/majority_element.py)                                    |                                                                                                                                   |

src/FractionToRecurringDecimal.java

@@ -0,0 +1,48 @@
+// https://leetcode.com/problems/fraction-to-recurring-decimal
+// T: O(log(n / d)) but not sure, could use some mathematician's help
+// S: O(log(n / d))
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class FractionToRecurringDecimal {
+    private static final String ZERO = "0";
+
+    public String fractionToDecimal(long numerator, long denominator) {
+        if (numerator == 0) return ZERO;
+
+        StringBuilder result = new StringBuilder();
+        result.append(isNegative(numerator, denominator) ? "-" : "");
+
+        numerator = Math.abs(numerator);
+        denominator = Math.abs(denominator);
+
+        // integral part
+        result.append(numerator / denominator);
+        numerator %= denominator;
+        if (numerator == 0) return result.toString();
+
+        // fractional part
+        result.append(".");
+        Map<Long, Integer> map = new HashMap<>();
+        map.put(numerator, result.length());
+
+        while (numerator != 0) {
+            numerator *= 10;
+            result.append(numerator / denominator);
+            numerator %= denominator;
+            if (map.containsKey(numerator)) {
+                int index = map.get(numerator);
+                result.insert(index, "(");
+                result.append(")");
+                break;
+            } else map.put(numerator, result.length());
+        }
+
+        return result.toString();
+    }
+
+    private boolean isNegative(long numerator, long denominator) {
+        return (numerator > 0) ^ (denominator > 0);
+    }
+}