增加代码

Author: starsingchow

java/141.环形链表.java

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+/*
+ * @lc app=leetcode.cn id=141 lang=java
+ *
+ * [141] 环形链表
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) {
+ *         val = x;
+ *         next = null;
+ *     }
+ * }
+ */
+public class Solution {
+    public boolean hasCycle(ListNode head) {
+        if(head == null) return false;
+        ListNode slow = head;
+        ListNode fast = head.next;
+
+        while(fast != null && fast.next != null) {
+            if(slow == fast) {
+                return true;
+            }
+
+            slow = slow.next;
+            fast = fast.next.next;
+        }
+
+        return false;
+    }
+}
+// @lc code=end
+

java/142.环形链表II.java

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+/*
+ * @lc app=leetcode.cn id=142 lang=java
+ *
+ * [142] 环形链表 II
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) {
+ *         val = x;
+ *         next = null;
+ *     }
+ * }
+ */
+public class Solution {
+    public ListNode detectCycle(ListNode head) {
+        if(head == null) return null;
+
+        ListNode slow = head;
+        ListNode fast = head;
+
+        while(fast != null && fast.next != null) {
+            fast = fast.next.next;
+            slow = slow.next;
+            if(slow == fast) {
+                fast = head;
+                while(fast != slow) {
+                    fast = fast.next;
+                    slow = slow.next;
+                }
+
+                return slow;
+            }
+        }
+
+        return null;
+    }
+}
+// @lc code=end
+

java/234.回文链表.java

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+/*
+ * @lc app=leetcode.cn id=234 lang=java
+ *
+ * [234] 回文链表
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    public boolean isPalindrome(ListNode head) {
+        if(head == null) return true;
+
+        ListNode slow = head;
+        ListNode fast = head.next;
+
+        while(fast != null && fast.next != null) {
+            slow = slow.next;
+            fast = fast.next.next;
+        }
+
+        ListNode tail = reverse(slow.next);
+        slow.next = null;
+
+        while(head != null && tail != null) {
+            if(head.val != tail.val) {
+                return false;
+            }
+
+            head = head.next;
+            tail = tail.next;
+        }
+
+        return true;
+        
+    }
+
+    private ListNode reverse(ListNode node) {
+        if(node == null) return null;
+
+        ListNode dummy = new ListNode();
+        while(node != null) {
+            ListNode tmp = node.next;
+            node.next = dummy.next;
+            dummy.next = node;
+            node = tmp;
+        }
+
+        return dummy.next;
+    }
+    
+    
+}
+// @lc code=end
+