adding Problem 24

能够通过测试，但是程序啰嗦了

Author: aQua

Algorithms/0024.swap-nodes-in-pairs/README.md

@@ -1,7 +1,12 @@
 # [24. Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/)
 
 ## 题目
+Given a linked list, swap every two adjacent nodes and return its head.
 
+For example,
+Given 1->2->3->4, you should return the list as 2->1->4->3.
+
+Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.
 
 ## 解题思路
 

Algorithms/0024.swap-nodes-in-pairs/swap-nodes-in-pairs.go

@@ -1,2 +1,35 @@
 package Problem0024
 
+// ListNode ListNode
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+func swapPairs(head *ListNode) *ListNode {
+	if head == nil || head.Next == nil {
+		return head
+	}
+
+	var cur *ListNode
+	head = swap(head)
+	cur = head.Next
+
+	for cur != nil && cur.Next != nil {
+		cur.Next = swap(cur.Next)
+		cur = cur.Next.Next
+	}
+
+	return head
+}
+
+func swap(l *ListNode) *ListNode {
+	if l.Next != nil {
+		temp := l.Next
+		l.Next = temp.Next
+		temp.Next = l
+		return temp
+	}
+
+	return l
+}

Algorithms/0024.swap-nodes-in-pairs/swap-nodes-in-pairs_test.go

@@ -1,8 +1,8 @@
 package Problem0024
 
 import (
-	"testing"
 	"fmt"
+	"testing"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -15,13 +15,13 @@ type question struct {
 // para 是参数
 // one 代表第一个参数
 type para struct {
-	one string
+	one []int
 }
 
 // ans 是答案
 // one 代表第一个答案
 type ans struct {
-	one string
+	one []int
 }
 
 func Test_Problem0024(t *testing.T) {
@@ -30,17 +30,68 @@ func Test_Problem0024(t *testing.T) {
 	qs := []question{
 
 		question{
-			para{""},
-			ans{""},
+			para{[]int{}},
+			ans{[]int{}},
 		},
-	
+
+		question{
+			para{[]int{1}},
+			ans{[]int{1}},
+		},
+
+		question{
+			para{[]int{1, 2, 3, 4}},
+			ans{[]int{2, 1, 4, 3}},
+		},
+
+		question{
+			para{[]int{1, 2, 3, 4, 5}},
+			ans{[]int{2, 1, 4, 3, 5}},
+		},
+
 		// 如需多个测试，可以复制上方元素。
 	}
 
 	for _, q := range qs {
 		a, p := q.ans, q.para
 		fmt.Printf("~~%v~~\n", p)
 
-		ast.Equal(a.one, (p.one), "输入:%v", p)
+		ast.Equal(a.one, l2s(swapPairs(s2l(p.one))), "输入:%v", p)
+	}
+}
+
+func Test_swap(t *testing.T) {
+	assert.Equal(t, []int{2, 1, 3, 4}, l2s(swap(s2l([]int{1, 2, 3, 4}))), "swap没能成功转换")
+}
+
+// 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
 }