add q25_k个一组翻转链表

README.md

@@ -10,6 +10,7 @@
 
 * [q2_两数相加](/src/链表操作/q2_两数相加)
 * [q19_删除链表的倒数第N个节点](/src/链表操作/q19_删除链表的倒数第N个节点)
+* [q25_k个一组翻转链表](/src/链表操作/q25_k个一组翻转链表)
 * [q61_旋转链表](/src/链表操作/q61_旋转链表)
 * [q138_复制带随机指针的链表](/src/链表操作/q138_复制带随机指针的链表)
 * [q206_反转链表](/src/链表操作/q206_反转链表)

src/链表操作/q25_k个一组翻转链表/ListNode.java

@@ -0,0 +1,12 @@
+package 链表操作.q25_k个一组翻转链表;
+
+
+public class ListNode {
+    int val;
+    ListNode next;
+
+    ListNode(int x) {
+        val = x;
+    }
+}
+

src/链表操作/q25_k个一组翻转链表/Solution.java

@@ -0,0 +1,42 @@
+package 链表操作.q25_k个一组翻转链表;
+
+public class Solution {
+
+    public ListNode reverseKGroup(ListNode head, int k) {
+        ListNode hair = new ListNode(0);
+        hair.next = head;
+
+        ListNode pre = hair;
+        ListNode end = hair;
+
+        while (end.next != null) {
+            for (int i = 0; i < k && end != null; i++){
+                end = end.next;
+            }
+            if (end == null){
+                break;
+            }
+            ListNode start = pre.next;
+            ListNode next = end.next;
+            end.next = null;
+            pre.next = reverse(start);
+            start.next = next;
+            pre = start;
+
+            end = pre;
+        }
+        return hair.next;
+    }
+
+    private ListNode reverse(ListNode head) {
+        ListNode pre = null;
+        ListNode curr = head;
+        while (curr != null) {
+            ListNode next = curr.next;
+            curr.next = pre;
+            pre = curr;
+            curr = next;
+        }
+        return pre;
+    }
+}