add: K个一组翻转链表

README.md

@@ -411,3 +411,8 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
 
   - LeetCode 876. 链表的中间结点 <https://leetcode-cn.com/problems/middle-of-the-linked-list/>
   - LintCode 1609. 链表的中间结点 <https://www.lintcode.com/problem/middle-of-the-linked-list/description>
+
+- [K个一组翻转链表](src/list/reverse-nodes-in-k-group.js)
+
+  - LeetCode 25. K 个一组翻转链表 <https://leetcode-cn.com/problems/reverse-nodes-in-k-group/>
+  - LintCode 450. K组翻转链表 <https://www.lintcode.com/problem/reverse-nodes-in-k-group/>

src/list/reverse-nodes-in-k-group.js

@@ -0,0 +1,49 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val) {
+ *     this.val = val;
+ *     this.next = null;
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @param {number} k
+ * @return {ListNode}
+ */
+export const reverseKGroup = function (head, k) {
+  let sum = 0
+  let start = head
+  let newStart = head
+  let first = true
+  const last = []
+  while (head) {
+    if (++sum === k) {
+      const headNext = head.next
+      last.push(start)
+      let next = head.next
+      for (let i = 0; i < sum - 1; i++) {
+        const tmp = start.next
+        start.next = next
+        next = start
+        start = tmp
+      }
+
+      start.next = next
+
+      if (first) {
+        newStart = start
+        first = false
+      } else {
+        const la = last.shift()
+        la.next = head
+      }
+      sum = 0
+      start = headNext
+      head = headNext
+    } else {
+      head = head.next
+    }
+  }
+
+  return newStart
+}

test/list/ListNode.js

@@ -15,3 +15,13 @@ export const arrToList = (arr) => {
 
   return head
 }
+
+export const listToArr = (list) => {
+  const arr = []
+  while (list) {
+    arr.push(list.val)
+    list = list.next
+  }
+
+  return arr
+}

test/list/reverse-nodes-in-k-group.test.js

@@ -0,0 +1,11 @@
+import { reverseKGroup } from '../../src/list/reverse-nodes-in-k-group'
+import { arrToList, listToArr } from './ListNode'
+
+test('K个一组翻转链表', () => {
+  const res = reverseKGroup(arrToList([1, 2, 3, 4, 5]), 3)
+  expect(listToArr(res)).toEqual([3, 2, 1, 4, 5])
+  expect(res).toEqual(arrToList([3, 2, 1, 4, 5]))
+  expect(reverseKGroup(arrToList([1, 2, 3, 4, 5]), 2)).toEqual(arrToList([2, 1, 4, 3, 5]))
+  expect(reverseKGroup(arrToList([1, 2, 3, 4, 5, 6]), 2)).toEqual(arrToList([2, 1, 4, 3, 6, 5]))
+  expect(reverseKGroup(arrToList([1, 2, 3, 4, 5, 6, 7, 8]), 2)).toEqual(arrToList([2, 1, 4, 3, 6, 5, 8, 7]))
+})