Merge pull request #1929 from josuebrunel/feat/0234-palindrome-linked-list.go

Create 0234-palindrome-linked-list.go

Author: tahsintunan

go/0234-palindrome-linked-list.go

@@ -0,0 +1,48 @@
+/**
+Move slow and fast pointer along the list.
+Slow pointer nodes are added to reversed list.
+When no more fast move is possible, iterate
+along slow and back along reversed list while
+checking for value equality
+
+Time: O(N)
+Space: O(1)
+**/
+
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+func isPalindrome(head *ListNode) bool {
+	slow, fast := head, head
+	var rev *ListNode
+
+	for fast != nil && fast.Next != nil {
+		fast = fast.Next.Next
+		next_slow := slow.Next
+		slow.Next = rev
+		rev = slow
+		slow = next_slow
+	}
+
+	// if fast is not null, slow is middle  of
+	// odd length list which is skipped
+	// if fast is null, slow is first element of
+	// the 2nd half of even length list
+	if fast != nil {
+		slow = slow.Next
+	}
+
+	for slow != nil {
+		if slow.Val != rev.Val {
+			return false
+		}
+		slow = slow.Next
+		rev = rev.Next
+	}
+
+	return true
+}