leetcode解题

141.linked-list-cycle.java

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+/*
+ * @lc app=leetcode id=141 lang=java
+ *
+ * [141] Linked List Cycle
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) {
+ *         val = x;
+ *         next = null;
+ *     }
+ * }
+ */
+public class Solution {
+    /**
+     * 快慢指针，若链表中存在环，则快指针一次动两步，慢指针一次动一步，快指针一定会赶上慢指针
+     * 
+     * @param head
+     * @return
+     */
+    public boolean hasCycle(ListNode head) {
+        ListNode slow = head, fast = head;
+        boolean isCycle = false;
+        while(fast != null && fast.next != null) {
+            fast = fast.next.next;
+            slow = slow.next;
+            if(fast == slow) {
+                isCycle = true;
+                break;
+            }
+        }
+        return isCycle;
+    }
+}
+// @lc code=end
+