연결리스트 - Two Pointer Technique (Leetcode)

https://leetcode.com/explore/learn/card/linked-list/214/two-pointer-technique/1212/

Author: codehumane

src/main/java/linkedlist/LinkedListCycle.java

@@ -0,0 +1,36 @@
+package linkedlist;
+
+public class LinkedListCycle {
+
+    public boolean hasCycle(ListNode head) {
+
+        ListNode faster = head;
+        ListNode slower = head;
+
+        while (faster != null && faster.next != null) {
+
+            faster = faster.next;
+            if (faster == slower) return true;
+
+            faster = faster.next;
+            if (faster == null) return false;
+            if (faster == slower) return true;
+
+            slower = slower.next;
+        }
+
+        return false;
+    }
+
+    public static class ListNode {
+
+        public int val;
+        public ListNode next;
+
+        public ListNode(int x) {
+            val = x;
+            next = null;
+        }
+    }
+}
+

src/test/java/linkedlist/LinkedListCycleTest.java

@@ -0,0 +1,70 @@
+package linkedlist;
+
+import lombok.val;
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class LinkedListCycleTest {
+
+    @Test
+    public void hasCycleExample1() {
+
+        // given: 3 -> 2 -> 0 -> -4 -> 2(cycle)
+        val node1 = new LinkedListCycle.ListNode(3);
+        val node2 = new LinkedListCycle.ListNode(2);
+        val node3 = new LinkedListCycle.ListNode(0);
+        val node4 = new LinkedListCycle.ListNode(-4);
+        node1.next = node2;
+        node2.next = node3;
+        node3.next = node4;
+        node4.next = node2;
+
+        // when
+        val hasCycle = new LinkedListCycle().hasCycle(node1);
+
+        // then
+        assertTrue(hasCycle);
+    }
+
+    @Test
+    public void hasCycleExample2() {
+
+        // given: 1 -> 2 -> 1(cycle)
+        val node1 = new LinkedListCycle.ListNode(1);
+        val node2 = new LinkedListCycle.ListNode(2);
+        node1.next = node2;
+        node2.next = node1;
+
+        // when
+        val hasCycle = new LinkedListCycle().hasCycle(node1);
+
+        // then
+        assertTrue(hasCycle);
+    }
+
+    @Test
+    public void hasCycleExample3() {
+
+        // given: 1
+        val node1 = new LinkedListCycle.ListNode(1);
+
+        // when
+        val hasCycle = new LinkedListCycle().hasCycle(node1);
+
+        // then
+        assertFalse(hasCycle);
+    }
+
+    @Test
+    public void hasCycleWhenHeadIsNull() {
+
+        // when
+        val hasCycle = new LinkedListCycle().hasCycle(null);
+
+        // then
+        assertFalse(hasCycle);
+    }
+
+}