Solve Problem 166 - Fraction To Recurring Decimal

Author: hieu

src/twopointers/slowfast/Problem166_FractionToRecurringDecimal.java

@@ -0,0 +1,103 @@
+package twopointers.slowfast;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class Problem166_FractionToRecurringDecimal {
+
+    public String fractionToDecimal1(int numerator, int denominator) {
+        if (denominator == 0) return "";
+        long m = (long)numerator, n = (long)denominator;
+        StringBuilder sb = new StringBuilder();
+
+        // handle sign
+        if (m > 0 && n < 0) {
+            sb.append('-');
+            n = -n;
+        }
+        if (m < 0 && n > 0) {
+            sb.append('-');
+            m = -m;
+        }
+
+        // handle integral part
+        sb.append(m/n);
+        m %= n;
+        if (m == 0) return sb.toString();
+
+        // handle fractional part
+        Map<Long, Integer> map = new HashMap<>();
+        sb.append('.');
+        map.put(m, sb.length());
+        while (m != 0) {
+            m *= 10;
+            sb.append(m/n);
+            m %= n;
+            if (map.containsKey(m)) {
+                int index = map.get(m);
+                sb.insert(index, '(');
+                sb.append(')');
+                break;
+            }
+            else {
+                map.put(m, sb.length());
+            }
+        }
+
+        return sb.toString();
+    }
+
+
+    public String fractionToDecimal(int numerator, int denominator) {
+        StringBuilder sb = new StringBuilder();
+        if ((numerator > 0 && denominator < 0) || (numerator < 0 && denominator > 0)) {
+            sb.append("-");
+        }
+        long nLong = Math.abs((long) numerator);
+        long dLong = Math.abs((long) denominator);
+        sb.append(nLong / dLong);
+        nLong %= dLong;
+        if (nLong == 0) {
+            return sb.toString();
+        }
+        sb.append('.');
+        nLong *= 10;
+
+        // cycle detection
+        long slow = nLong;
+        long fast = nLong;
+        while (fast != 0) {
+            slow = next(slow, dLong);
+            fast = next(next(fast, dLong), dLong);
+            if (slow == fast) break;
+        }
+        // 2 cases: slow == fast or fast == 0
+        slow = nLong;
+        if (fast == 0) {
+            while (slow != 0) {
+                sb.append(slow / dLong);
+                slow = next(slow, dLong);
+            }
+            return sb.toString();
+        }
+        // has cycle
+        while (slow != fast) {
+            sb.append(slow / dLong);
+            slow = next(slow, dLong);
+            fast = next(fast, dLong);
+        }
+        long cycleStart = slow;
+        sb.append("(");
+        do {
+            sb.append(slow / dLong);
+            slow = next(slow, dLong);
+        } while (slow != cycleStart);
+        sb.append(")");
+        return sb.toString();
+    }
+
+    private long next(long numerator, long denominator) {
+        numerator %= denominator;
+        return numerator * 10;
+    }
+}

src/twopointers/Problem457_CircularArrayLoop.java renamed to src/twopointers/slowfast/Problem457_CircularArrayLoop.java

@@ -1,4 +1,4 @@
-package twopointers;
+package twopointers.slowfast;
 
 public class Problem457_CircularArrayLoop {