feat: solve reverse linked list

Author: GangBean

reverse-linked-list/GangBean.java

@@ -0,0 +1,42 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    /**
+    1. strategy
+    - iterate over all Node, save value to list
+    - iterate list in reverse order, create Node and link
+    2. complexity
+    - time: O(N)
+    - space: O(N)
+     */
+    public ListNode reverseList(ListNode head) {
+        List<Integer> list = new ArrayList<>();
+
+        while (head != null) {
+            list.add(head.val);
+            head = head.next;
+        }
+
+        ListNode prev = new ListNode();
+        ListNode ret = null;
+
+        for (int i=list.size()-1; i>=0; i--) {
+            ListNode node = new ListNode(list.get(i));
+            prev.next = node;
+            prev = prev.next;
+            if (ret == null) {
+                ret = prev;
+            }
+        }
+        return ret;
+    }
+}
+