note

Author: guangxush

guangxu/202012/20201202.md

@@ -1,11 +1,51 @@
 ## Algorithm
 
+[206. Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)
+
 ### Description
 
-### Solution
+Reverse a singly linked list.
+
+Example:
 
-```java 
+```
+Input: 1->2->3->4->5->NULL
+Output: 5->4->3->2->1->NULL
+```
+
+Follow up:
+
+A linked list can be reversed either iteratively or recursively. Could you implement both?
+
+### Solution
 
+```java
+/**
+ * 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 ListNode reverseList(ListNode head){
+        if(head == null || head.next == null){
+            return head;
+        }
+        ListNode pre = null;
+        ListNode now = head;
+        while(now!=null){
+            ListNode next = now.next;
+            now.next = pre;
+            pre = now;
+            now = next;
+        }
+        return pre;
+    }
+}
 ```
 
 ### Discuss

guangxu/202012/20201203.md

@@ -1,15 +1,85 @@
 ## Algorithm
 
+[234. Palindrome Linked List](https://leetcode.com/problems/palindrome-linked-list/)
+
 ### Description
 
-### Solution
+Given a singly linked list, determine if it is a palindrome.
 
-```java 
+Example 1:
+```
+Input: 1->2
+Output: false
+```
 
+Example 2:
+```
+Input: 1->2->2->1
+Output: true
+```
+
+Follow up:
+- Could you do it in O(n) time and O(1) space?
+
+### Solution
+
+```java
+/**
+ * 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 {
+    private ListNode reverseList(ListNode head){
+        ListNode pre = null;
+        ListNode now = head;
+        while(now!=null){
+            ListNode next = now.next;
+            now.next = pre;
+            pre = now;
+            now = next;
+        }
+        return pre;
+    }
+    private boolean isEqual(ListNode h1, ListNode h2) {
+        while(h1!=null&&h2!=null){
+            if(h1.val!=h2.val){
+                return false;
+            }
+            h1 = h1.next;
+            h2 = h2.next;
+        }
+        return true;
+    }
+    public boolean isPalindrome(ListNode head) {
+        if(head == null || head.next==null){
+            return true;
+        }
+        ListNode slow = head;
+        ListNode fast = head;
+        while(fast!=null&&fast.next!=null&&fast.next.next!=null){
+            slow = slow.next;
+            fast = fast.next.next;
+        }
+        ListNode firstHalfHead = head;
+        ListNode firstHalfTail = slow;
+        ListNode secondHalfHead = reverseList(firstHalfTail.next);
+        boolean result = isEqual(firstHalfHead, secondHalfHead);
+        reverseList(firstHalfTail.next);
+        return result;
+    }
+}
 ```
 
 ### Discuss
 
+找中点+链表反转+遍历是否相等
+
 ## Review
 
 

guangxu/202012/20201204.md

@@ -1,15 +1,96 @@
 ## Algorithm
 
+[237. Delete Node in a Linked List](https://leetcode.com/problems/delete-node-in-a-linked-list/)
+
 ### Description
 
-### Solution
+Write a function to delete a node in a singly-linked list. You will not be given access to the head of the list, instead you will be given access to the node to be deleted directly.
+
+It is guaranteed that the node to be deleted is not a tail node in the list.
+
+Example 1:
+
+![](assets/20201204-02e2e166.png)
+
+```
+Input: head = [4,5,1,9], node = 5
+Output: [4,1,9]
+Explanation: You are given the second node with value 5, the linked list should become 4 -> 1 -> 9 after calling your function.
+```
+
+Example 2:
+
+![](assets/20201204-59644db6.png)
+
+```
+Input: head = [4,5,1,9], node = 1
+Output: [4,5,9]
+Explanation: You are given the third node with value 1, the linked list should become 4 -> 5 -> 9 after calling your function.
+```
+
+Example 3:
+
+```
+Input: head = [1,2,3,4], node = 3
+Output: [1,2,4]
+```
 
-```java 
+Example 4:
 
 ```
+Input: head = [0,1], node = 0
+Output: [1]
+```
+
+Example 5:
+
+```
+Input: head = [-3,5,-99], node = -3
+Output: [5,-99]
+```
+
+Constraints:
+
+- The number of the nodes in the given list is in the range [2, 1000].
+- -1000 <= Node.val <= 1000
+- The value of each node in the list is unique.
+- The node to be deleted is in the list and is not a tail node
+
+### Solution
+
+```java
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+ class Solution {
+   public void deleteNode(ListNode node) {
+      ListNode curr = node;
+      ListNode nxt = node.next;
+      if(nxt != null){
+          curr.val = nxt.val;
+          curr.next = nxt.next;
+       }        
+   }
+ }
+```
 
 ### Discuss
 
+这道题完全没有给除了目标节点以外的任何参数，必须通过修改val的值来实现删除节点。
+
+1. 把node.next的值赋给node
+
+2. 把node.next指向node.next.next
+
+其实相当于删除node.next
+
+
+
 ## Review
 
 

guangxu/202012/assets/20201204-02e2e166.png

@@ -1,7 +1,9 @@
 | 标题 | Algorithm | Review | Tip | Share|
 | :-----| :---- | :---- |  :---- |  :---- |
-| [20201201](./202012/20201201.md) |[141. Linked List Cycle（判断链表中是否有环）](https://leetcode.com/problems/linked-list-cycle/)
-|||
+| [20201204](./202012/20201204.md) |[237. Delete Node in a Linked List(删除链表中的一个节点)](https://leetcode.com/problems/delete-node-in-a-linked-list/)|||
+| [20201203](./202012/20201203.md) |[234. Palindrome Linked List(回文链表)](https://leetcode.com/problems/palindrome-linked-list/)|||
+| [20201202](./202012/20201202.md) |[206. Reverse Linked List（链表反转）](https://leetcode.com/problems/reverse-linked-list/)|||
+| [20201201](./202012/20201201.md) |[141. Linked List Cycle（判断链表中是否有环）](https://leetcode.com/problems/linked-list-cycle/)|||
 | [20201130](./202011/20201130.md) |[142. Linked List Cycle II(找链表环的交点)](https://leetcode.com/problems/linked-list-cycle-ii/)|||
 | [20201129](./202011/20201129.md) |[146. LRU Cache](https://leetcode.com/problems/lru-cache/)|||
 | [20201128](./202011/20201128.md) |[199. Binary Tree Right Side View (二叉树右视图)](https://leetcode.com/problems/binary-tree-right-side-view/)|||
@@ -24,7 +26,7 @@
 | [20201111](./202011/20201111.md) |[103. Binary Tree Zigzag Level Order Traversal（之字形打印二叉树）](https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/)|||
 | [20201110](./202011/20201110.md) |[102. Binary Tree Level Order Traversal（二叉树层次遍历）](https://leetcode.com/problems/binary-tree-level-order-traversal/)|||
 | [20201109](./202011/20201109.md) |[239. Sliding Window Maximum（滑动窗口最大值）](https://leetcode.com/problems/sliding-window-maximum/)|||
-| [20201108](./202011/20201108.md) |[72. Edit Distance](https://leetcode.com/problems/edit-distance/)|||
+| [20201108](./202011/20201108.md) |[72. Edit Distance（编辑距离）](https://leetcode.com/problems/edit-distance/)|||
 | [20201107](./202011/20201107.md) |[5. Longest Palindromic Substring(最长回文串)](https://leetcode.com/problems/longest-palindromic-substring/)|希尔排序||
 | [20201106](./202011/20201106.md) |[69. Sqrt(x)(折半查找求根号)](https://leetcode.com/problems/sqrtx/)|选择排序||
 | [20201105](./202011/20201105.md) |[62. Unique Paths（不同路径）](https://leetcode.com/problems/unique-paths/)|插入排序|||