添加 problem 24

Algorithms/24.Swap-Nodes-in-Pairs/README.md

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+# [24. Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/description/)
+
+## 题目
+
+Given a linked list, swap every two adjacent nodes and return its head.
+
+Example:
+
+Given 1->2->3->4, you should return the list as 2->1->4->3.
+Note:
+
+Your algorithm should use only constant extra space.
+You may not modify the values in the list's nodes, only nodes itself may be changed.
+
+## 题目大意
+
+两两相邻的元素，翻转链表

Algorithms/24.Swap-Nodes-in-Pairs/Swap Nodes in Pairs.go

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+package leetcode
+
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+
+func swapPairs(head *ListNode) *ListNode {
+	if head == nil || head.Next == nil {
+		return head
+	}
+	s := head.Next
+	var behind *ListNode
+	for head.Next != nil {
+		headNext := head.Next
+		if behind != nil && behind.Next != nil {
+			behind.Next = headNext
+		}
+		var next *ListNode
+		if head.Next.Next != nil {
+			next = head.Next.Next
+		}
+		if head.Next.Next != nil {
+			head.Next = next
+		} else {
+			head.Next = nil
+		}
+		headNext.Next = head
+		behind = head
+		if head.Next != nil {
+			head = next
+		}
+	}
+	return s
+}

Algorithms/24.Swap-Nodes-in-Pairs/Swap Nodes in Pairs_test.go

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+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question24 struct {
+	para24
+	ans24
+}
+
+// para 是参数
+// one 代表第一个参数
+type para24 struct {
+	one []int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans24 struct {
+	one []int
+}
+
+func Test_Problem24(t *testing.T) {
+
+	qs := []question24{
+
+		question24{
+			para24{[]int{}},
+			ans24{[]int{}},
+		},
+
+		question24{
+			para24{[]int{1}},
+			ans24{[]int{1}},
+		},
+
+		question24{
+			para24{[]int{1, 2, 3, 4}},
+			ans24{[]int{2, 1, 4, 3}},
+		},
+
+		question24{
+			para24{[]int{1, 2, 3, 4, 5}},
+			ans24{[]int{2, 1, 4, 3, 5}},
+		},
+
+		// 如需多个测试，可以复制上方元素。
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 24------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans24, q.para24
+		fmt.Printf("【input】:%v       【output】:%v\n", p, L2s(swapPairs(S2l(p.one))))
+	}
+	fmt.Printf("\n\n\n")
+}
+
+// convert *ListNode to []int
+func L2s(head *ListNode) []int {
+	res := []int{}
+
+	for head != nil {
+		res = append(res, head.Val)
+		head = head.Next
+	}
+
+	return res
+}
+
+// convert []int to *ListNode
+func S2l(nums []int) *ListNode {
+	if len(nums) == 0 {
+		return nil
+	}
+
+	res := &ListNode{
+		Val: nums[0],
+	}
+	temp := res
+	for i := 1; i < len(nums); i++ {
+		temp.Next = &ListNode{
+			Val: nums[i],
+		}
+		temp = temp.Next
+	}
+
+	return res
+}