Update solution 0234

leetcode/0234.Palindrome-Linked-List/234. Palindrome Linked List.go

@@ -15,22 +15,75 @@ type ListNode = structures.ListNode
  * }
  */
 
-func isPalindrome234(head *ListNode) bool {
+// 解法一
+func isPalindrome(head *ListNode) bool {
 	slice := []int{}
-
 	for head != nil {
 		slice = append(slice, head.Val)
 		head = head.Next
 	}
-
 	for i, j := 0, len(slice)-1; i < j; {
 		if slice[i] != slice[j] {
 			return false
 		}
-
 		i++
 		j--
 	}
-
 	return true
 }
+
+// 解法二
+// 此题和 143 题 Reorder List 思路基本一致
+func isPalindrome1(head *ListNode) bool {
+	if head == nil || head.Next == nil {
+		return true
+	}
+	res := true
+	// 寻找中间结点
+	p1 := head
+	p2 := head
+	for p2.Next != nil && p2.Next.Next != nil {
+		p1 = p1.Next
+		p2 = p2.Next.Next
+	}
+	// 反转链表后半部分  1->2->3->4->5->6 to 1->2->3->6->5->4
+	preMiddle := p1
+	preCurrent := p1.Next
+	for preCurrent.Next != nil {
+		current := preCurrent.Next
+		preCurrent.Next = current.Next
+		current.Next = preMiddle.Next
+		preMiddle.Next = current
+	}
+	// 扫描表，判断是否是回文
+	p1 = head
+	p2 = preMiddle.Next
+	// fmt.Printf("p1 = %v p2 = %v preMiddle = %v head = %v\n", p1.Val, p2.Val, preMiddle.Val, L2ss(head))
+	for p1 != preMiddle {
+		// fmt.Printf("*****p1 = %v p2 = %v preMiddle = %v head = %v\n", p1, p2, preMiddle, L2ss(head))
+		if p1.Val == p2.Val {
+			p1 = p1.Next
+			p2 = p2.Next
+			// fmt.Printf("-------p1 = %v p2 = %v preMiddle = %v head = %v\n", p1, p2, preMiddle, L2ss(head))
+		} else {
+			res = false
+			break
+		}
+	}
+	if p1 == preMiddle {
+		if p2 != nil && p1.Val != p2.Val {
+			return false
+		}
+	}
+	return res
+}
+
+// L2ss define
+func L2ss(head *ListNode) []int {
+	res := []int{}
+	for head != nil {
+		res = append(res, head.Val)
+		head = head.Next
+	}
+	return res
+}

leetcode/0234.Palindrome-Linked-List/234. Palindrome Linked List_test.go

@@ -83,7 +83,7 @@ func Test_Problem234(t *testing.T) {
 
 	for _, q := range qs {
 		_, p := q.ans234, q.para234
-		fmt.Printf("【input】:%v       【output】:%v\n", p, isPalindrome234(structures.Ints2List(p.one)))
+		fmt.Printf("【input】:%v       【output】:%v\n", p, isPalindrome(structures.Ints2List(p.one)))
 	}
 	fmt.Printf("\n\n\n")
 }