add: linked-list-cycle

Author: Yongseok-Choi-dev

linked-list-cycle/Solution.java

@@ -0,0 +1,67 @@
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+public class Solution {
+    public boolean hasCycle(ListNode head) {
+        Set<ListNode> nSet = new HashSet<>();
+
+        while (head != null) {
+            if (nSet.contains(head)) {
+                return true;
+            }
+
+            nSet.add(head);
+            head = head.next;
+        }
+
+        return false;
+    }
+}
+
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ * int val;
+ * ListNode next;
+ * ListNode(int x) {
+ * val = x;
+ * next = null;
+ * }
+ * }
+ */
+// NOTE: 같은 val의 다른 Node의 경우를 고려하지 못했다
+class WrongSolution {
+    public boolean hasCycle(ListNode head) {
+        Map<Integer, List<Integer>> vMap = new HashMap<>(); // NOTE: val, pos
+
+        if (head == null) {
+            return false;
+        }
+
+        ListNode cur = head;
+        boolean isCyclick = false;
+        int pos = -1;
+        while (cur != null) {
+
+            if (vMap.containsKey(cur.val)) {
+                isCyclick = true;
+                break;
+            }
+
+            List<Integer> posList = new ArrayList<>();
+            posList.add(pos++);
+            vMap.put(cur.val, posList);
+            cur = head.next;
+        }
+
+        if (isCyclick) {
+            return true;
+        } else {
+            return false;
+        }
+    }
+}