reverse linked list solution

Author: yhkee0404

reverse-linked-list/yhkee0404.dart

@@ -0,0 +1,20 @@
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *   int val;
+ *   ListNode? next;
+ *   ListNode([this.val = 0, this.next]);
+ * }
+ */
+class Solution {
+  ListNode? reverseList(ListNode? head) {
+    var u = null; // S(n) = O(1)
+    while (head != null) { // T(n) = O(n)
+        final temp = head.next;
+        head.next = u;
+        u = head;
+        head = temp;
+    }
+    return u;
+  }
+}