添加 problem 25

Algorithms/25.Reverse-Nodes-in-k-Group/README.md

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+# [25. Reverse Nodes in k-Group](https://leetcode.com/problems/reverse-nodes-in-k-group/description/)
+
+## 题目
+
+Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.
+
+k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it is.
+
+Example:
+
+Given this linked list: 1->2->3->4->5
+
+For k = 2, you should return: 2->1->4->3->5
+
+For k = 3, you should return: 3->2->1->4->5
+
+Note:
+
+Only constant extra memory is allowed.
+You may not alter the values in the list's nodes, only nodes itself may be changed.
+
+
+## 题目大意
+
+这一题是 problem 24 的加强版，problem 24 是两两相邻的元素，翻转链表。而 problem 25 要求的是 k 个相邻的元素，翻转链表，problem 相当于是 k = 2 的特殊情况。
+

Algorithms/25.Reverse-Nodes-in-k-Group/Reverse Nodes in k-Group.go

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+package leetcode
+
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+func reverseKGroup(head *ListNode, k int) *ListNode {
+	node := head
+	for i := 0; i < k; i++ {
+		if node == nil {
+			return head
+		}
+		node = node.Next
+	}
+	newHead := reverse(head, node)
+	head.Next = reverseKGroup(node, k)
+	return newHead
+}
+
+func reverse(first *ListNode, last *ListNode) *ListNode {
+	prev := last
+	for first != last {
+		tmp := first.Next
+		first.Next = prev
+		prev = first
+		first = tmp
+	}
+	return prev
+}

Algorithms/25.Reverse-Nodes-in-k-Group/Reverse Nodes in k-Group_test.go

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+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question25 struct {
+	para25
+	ans25
+}
+
+// para 是参数
+// one 代表第一个参数
+type para25 struct {
+	one []int
+	two int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans25 struct {
+	one []int
+}
+
+func Test_Problem25(t *testing.T) {
+
+	qs := []question25{
+
+		question25{
+			para25{
+				[]int{1, 2, 3, 4, 5},
+				3,
+			},
+			ans25{[]int{3, 2, 1, 4, 5}},
+		},
+
+		question25{
+			para25{
+				[]int{1, 2, 3, 4, 5},
+				1,
+			},
+			ans25{[]int{1, 2, 3, 4, 5}},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 25------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans25, q.para25
+		fmt.Printf("【input】:%v       【output】:%v\n", p, L2s(reverseKGroup(S2l(p.one), p.two)))
+	}
+	fmt.Printf("\n\n\n")
+}