Merge pull request #1890 from Lustellz/main

[Lustellz] WEEK 07 solution

Author: SamTheKorean

reverse-linked-list/Lustellz.ts

@@ -0,0 +1,26 @@
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+// Runtime: 0ms
+// Memory: 58.86MB
+
+function reverseList(head: ListNode | null): ListNode | null {
+    let previousNode: ListNode | null = null;
+    let currentNode: ListNode | null = head;
+    while(currentNode){
+        const nextNode: ListNode | null = currentNode.next; // mark nextNode's value of current node temporary
+        currentNode.next = previousNode; // set next node of current as previous node
+        previousNode = currentNode; // set previous node as current node
+        currentNode = nextNode; // move to nextNode
+    }
+    return previousNode // currentNode would be null if it reaches the end of the node list
+};