[ PS ] : Reverse Linked List

Author: uraflower

reverse-linked-list/uraflower.js

@@ -0,0 +1,48 @@
+function ListNode(val, next) {
+    this.val = (val === undefined ? 0 : val)
+    this.next = (next === undefined ? null : next)
+}
+
+// 첫 번째 시도
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
+/**
+ * 단방향 연결 리스트를 reverse하여 반환하는 함수
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+const reverseList = function (head) {
+    const newHead = new ListNode();
+
+    function _reverseList(head) {
+        if (!head) {
+            return newHead;
+        }
+
+        const reversedHead = _reverseList(head.next);
+        reversedHead.next = new ListNode(head.val, null);
+
+        return reversedHead.next;
+    }
+
+    _reverseList(head);
+    return newHead.next;
+};
+
+
+// 두 번째 시도
+// 시간복잡도: O(n)
+// 공간복잡도: O(1)
+const reverseList = function (head) {
+    let current = head;
+    let prev = null;
+
+    while (current) {
+        const next = current.next;
+        current.next = prev;
+        prev = current;
+        current = next;
+    }
+
+    return prev;
+};