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Author: whd

141 Linked List Cycle .cpp

@@ -0,0 +1,29 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    bool hasCycle(ListNode *head) {
+        ListNode *p = head, *q = head;
+        auto next = [] (ListNode *x) {
+            if (!x) {
+                return x;
+            }
+            return x->next;
+        };
+        while (p && q) {
+            p = next(p);
+            q = next(q);
+            q = next(q);
+            if (p && q && p == q) {
+                return true;
+            }
+        }
+        return false;
+    }
+};