2026-03-24 00:04

Author: SilverRainZ

src/p/leetcode/index.rst

@@ -275,7 +275,7 @@ Invert Binary Tree
    :diffculty: Easy
    :language: go
    :key: 二叉树
-   :date: 2021-07-07
+   :date: 2021-07-07 2026-03-23
 
 我能去 Google 了吗？[#]_
 
@@ -691,9 +691,12 @@ Reverse Linked List
 递归
    万万没想到……递归我没写出来。看题解，题解说很明白了。
 
+   2026-03-23: 写出来了
+
 迭代
    拿个栈。
 
+   2026-03-23: 存 cur 和 next 两个指针。
 
 Reverse Linked List II
 ----------------------

src/p/leetcode/invert-binary-tree/main.go

@@ -1,19 +1,19 @@
 package main
 
-//  for a binary tree node.
+// for a binary tree node.
 type TreeNode struct {
 	Val   int
 	Left  *TreeNode
 	Right *TreeNode
 }
 
 func invertTree(root *TreeNode) *TreeNode {
-	if root != nil {
-		l := root.Left
-		r := root.Right
-		root.Left = invertTree(r)
-		root.Right = invertTree(l)
+	if root == nil {
+		return nil
 	}
+	l, r := root.Left, root.Right
+	root.Left = invertTree(r)
+	root.Right = invertTree(l)
 	return root
 }
 

src/p/leetcode/reverse-linked-list/main.go

@@ -44,6 +44,23 @@ func reverseList2(head *ListNode) *ListNode {
 	return head
 }
 
+// 迭代法，存两个指针。
+func reverseList3(head *ListNode) *ListNode {
+	if head == nil || head.Next == nil {
+		return head
+	}
+	cur := head
+	next := head.Next
+	for next != nil {
+		nextnext := next.Next
+		next.Next = cur
+		cur = next
+		next = nextnext
+	}
+	head.Next = nil
+	return cur
+}
+
 func main() {
 	a := reverseList(&ListNode{Val: 1, Next: &ListNode{Val: 2}})
 	for a != nil {
@@ -55,4 +72,9 @@ func main() {
 		fmt.Println(a)
 		a = a.Next
 	}
+	a = reverseList3(&ListNode{Val: 1, Next: &ListNode{Val: 2}})
+	for a != nil {
+		fmt.Println(a)
+		a = a.Next
+	}
 }