Update 0206.翻转链表.md

添加 0206.翻转链表 Java版本

problems/0206.翻转链表.md

@@ -102,7 +102,47 @@ public:
 
 
 Java：
+```java
+class Solution {
+    // 双指针
+    public ListNode reverseList(ListNode head) {
+        ListNode prev = null;
+        ListNode cur = head;
+        ListNode temp = null;
+        while (cur != null) {
+            temp = cur.next;// 保存下一个节点
+            cur.next = prev;
+            prev = cur;
+            cur = temp;
+        }
+        return prev;
+    }
+}
+```
 
+```java
+class Solution {
+    /**
+     * 递归
+     */
+    public ListNode reverseList(ListNode head) {
+        return reverse(null, head);
+    }
+
+    private ListNode reverse(ListNode prev, ListNode cur) {
+        if (cur == null) {
+            return prev;
+        }
+        ListNode temp = null;
+        temp = cur.next;// 先保存下一个节点
+        cur.next = prev;// 反转
+        // 更新prev、cur位置
+        prev = cur;
+        cur = temp;
+        return reverse(prev, cur);
+    }
+}
+```
 
 Python：