142. shadowing

142/142. shadowing.md

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+# (Linked List Cycle II) [https://leetcode.com/problems/linked-list-cycle-ii/description/]
+# language: C++
+
+* 今回はset
+
+```cpp
+#include <iostream>
+#include <set>
+
+struct ListNode {
+    int val;
+    ListNode* next;
+    ListNode(int x) : val(x), next(nullptr) {}
+};
+
+class Solution {
+ public:
+    ListNode *detectCycle(ListNode *head) {
+        std::set<ListNode*> reached;
+        ListNode* node = head;
+        while (node) {
+            if (reached.contains(node)) {
+                return node;
+            }
+            reached.insert(node);
+            node = node->next;
+        }
+        return nullptr;
+    }
+};
+```
+