Solve Problem 457 - Circular Array Loop

Author: Hieu Luong

src/twopointers/Problem457_CircularArrayLoop.java

@@ -0,0 +1,40 @@
+package twopointers;
+
+public class Problem457_CircularArrayLoop {
+
+    public boolean circularArrayLoop(int[] A) {
+        for (int i = 0; i < A.length; i++) {
+            if (A[i] == 0) continue;
+            int a = A[i];
+
+            int slow = i, fast = next(A,i);
+            while (same(a, A[fast]) && same(a, A[next(A, fast)])) {
+                if (slow == fast) {
+                    if (slow == next(A, slow)) break;
+                    return true;
+                }
+                slow = next(A, slow);
+                fast = next(A, next(A, fast));
+            }
+
+            slow = i;
+            while (same(a, A[slow])) {
+                int tmp = next(A, slow);
+                A[slow] = 0;
+                slow = tmp;
+            }
+        }
+        return false;
+    }
+
+    private int next(int[] A, int i) {
+        int n = A.length, j = (i + A[i]) % n;
+        return (j >= 0) ? j : j+n;
+    }
+
+    private boolean same(int a, int b) {
+        if (a > 0 && b > 0) return true;
+        if (a < 0 && b < 0) return true;
+        return false;
+    }
+}