finish Problem 206

做25题的时候,需要逆转链,发现这正好就是206题,就先把206解决了.

Author: aQua

Algorithms/0025.reverse-nodes-in-k-group/reverse-nodes-in-k-group.go

@@ -11,9 +11,34 @@ func reverseKGroup(head *ListNode, k int) *ListNode {
 
 	return nil
 }
+func canReverse(head *ListNode, k int) (*ListNode, bool) {
+	for head != nil {
+		k--
+		if k == 0 {
+			return head.Next, true
+		}
+	}
+	return nil, false
+}
+
+func reverse(head *ListNode) (first, last *ListNode) {
+	if head == nil || head.Next == nil {
+		return head, nil
+	}
+	if head.Next.Next == nil {
+		last = head
+		first = head.Next
+		first.Next = last
+	}
+	var temp *ListNode
+	last = head
+	first, temp = reverse(head.Next)
+	temp.Next = last
+	//last.Next = nil
+	return first, last
+}
 
 // ListNode 是链接节点
-// 这个不能复制到*_test.go文件中。会导致Travis失败
 type ListNode struct {
 	Val  int
 	Next *ListNode

Algorithms/0025.reverse-nodes-in-k-group/reverse-nodes-in-k-group_test.go

@@ -45,10 +45,15 @@ func Test_Problem0025(t *testing.T) {
 		a, p := q.ans, q.para
 		fmt.Printf("~~%v~~\n", p)
 
-		ast.Equal(a.one, l2s(reverseKGroup(s2l (p.one),p.two)), "输入:%v", p)
+		ast.Equal(a.one, l2s(reverseKGroup(s2l(p.one), p.two)), "输入:%v", p)
 	}
 }
 
+func Test_reverse(t *testing.T) {
+	head, _ := reverse(s2l([]int{1, 2, 3}))
+	assert.Equal(t, []int{3, 2, 1}, l2s(head), "无法逆转链")
+}
+
 // convert *ListNode to []int
 func l2s(head *ListNode) []int {
 	res := []int{}

Algorithms/0206.reverse-linked-list/README.md

@@ -1,10 +1,10 @@
 # [206. Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)
 
 ## 题目
-
+Reverse a singly linked list.
 
 ## 解题思路
-
+详见注释
 
 ## 总结
 

Algorithms/0206.reverse-linked-list/reverse-linked-list.go

@@ -1,2 +1,26 @@
 package Problem0206
 
+func reverseList(head *ListNode) *ListNode {
+	// prev 是所有已经逆转的节点的head
+	var prev *ListNode
+
+	// head 是下一个被逆转的节点
+	for head != nil {
+		// 让temp指向head.Next, 免得head.Next不见了.
+		temp := head.Next
+		// head称为已经逆转的节点的新head
+		head.Next = prev
+		// 让prev重新称为所有已被逆转节点的head
+		prev = head
+		// 让head指向下一个被逆转的节点
+		head = temp
+	}
+
+	return prev
+}
+
+// ListNode 是链接节点
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}

Algorithms/0206.reverse-linked-list/reverse-linked-list_test.go

@@ -1,8 +1,8 @@
 package Problem0206
 
 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_Problem0206(t *testing.T) {
@@ -30,17 +30,49 @@ func Test_Problem0206(t *testing.T) {
 	qs := []question{
 
 		question{
-			para{""},
-			ans{""},
+			para{[]int{1, 2, 3, 4, 5}},
+			ans{[]int{5, 4, 3, 2, 1}},
 		},
-	
+
 		// 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(reverseList(s2l(p.one))), "输入:%v", p)
+	}
+}
+
+// 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
 }