9주차

Author: jdalma

linked-list-cycle/jdalma.kt

@@ -0,0 +1,45 @@
+package leetcode_study
+
+import io.kotest.matchers.shouldBe
+import org.junit.jupiter.api.Test
+
+class `linked-list-cycle` {
+
+    data class ListNode(var `val`: Int) {
+        var next: ListNode? = null
+    }
+
+    /**
+     * TC: O(n), SC: O(1)
+     */
+    fun hasCycle(head: ListNode?): Boolean {
+        if (head == null) return false
+
+        var slow = head
+        var fast = head
+
+        while (fast?.next != null) {
+            slow = slow?.next
+            fast = fast.next?.next
+
+            if (slow == fast) return true
+        }
+
+        return false
+    }
+
+    @Test
+    fun `입력받은 노드에 사이클이 존재한다면 참을 반환한다`() {
+        val three = ListNode(3)
+        val two = ListNode(2)
+        val zero = ListNode(0)
+        val four = ListNode(4)
+
+        three.next = two
+        two.next = zero
+        zero.next = four
+        four.next = two
+
+        hasCycle(three) shouldBe true
+    }
+}