add leetcode 143

Author: saenaii

src/0143.Reorder-List/ListNode.go

@@ -0,0 +1,61 @@
+package Solution
+
+import (
+	"fmt"
+	"math/rand"
+)
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+//	比较结果
+func isEqual(l1 *ListNode, l2 *ListNode) bool {
+
+	for l1 != nil && l2 != nil {
+		if l1.Val != l2.Val {
+			return false
+		}
+		l1 = l1.Next
+		l2 = l2.Next
+	}
+	if l1 == nil && l2 != nil {
+		return false
+	}
+	if l1 != nil && l2 == nil {
+		return false
+	}
+	return true
+}
+
+func PrintList(head *ListNode) {
+	for head != nil {
+		fmt.Print(head.Val, "->")
+		head = head.Next
+	}
+	fmt.Println()
+}
+
+// 根据数组反序列化链表
+func UnmarshalListBySlice(nums []int) *ListNode {
+	head := &ListNode{Val: -1, Next: nil}
+	tmp := head
+	for _, v := range nums {
+		tmp.Next = &ListNode{Val: v, Next: nil}
+		tmp = tmp.Next
+	}
+	return head.Next
+}
+
+// 随机初始化链表
+func UnmarshalListByRand(max_num int, len int) *ListNode {
+	head := &ListNode{Val: -1, Next: nil}
+	tmp := head
+
+	for i := 0; i < len; i++ {
+		tmp.Next = &ListNode{Val: rand.Intn(max_num), Next: nil}
+		tmp = tmp.Next
+	}
+	return head.Next
+}

src/0143.Reorder-List/README.md

@@ -0,0 +1,84 @@
+# [143. Reorder List][title]
+
+## Description
+Given a singly linked list L: L0→L1→…→Ln-1→Ln,
+reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…
+
+You may not modify the values in the list's nodes, only nodes itself may be changed.
+
+**Example 1:**
+```
+Given 1->2->3->4, reorder it to 1->4->2->3.
+```
+
+**Example 2:**
+```
+Given 1->2->3->4->5, reorder it to 1->5->2->4->3.
+```
+
+**Tags:** Linked List
+
+## 题意
+> 给定一个单链表，对链表进行重新排序。
+
+## 题解
+> 把链表分成两部分，对后半段链表进行逆序，然后再将两部分合并。
+
+### 思路1
+1. 找到链表的中点，将链表拆分成前后两部分。
+1. 对后半段链表进行逆序操作。
+1. 将前半段链表和逆序后的后半段链表合并。
+
+```go
+func reorderList(head *ListNode)  {
+    if nil == head || nil == head.Next {
+        return
+    }
+    mid := findMid(head)
+    first, second := head, reverseList(mid.Next)
+    mid.Next = nil
+    
+    newHead := new(ListNode)
+    current := newHead
+    for first != nil || second != nil {
+        if first != nil {
+            current.Next = &ListNode{first.Val, nil}
+            current = current.Next
+            first = first.Next
+        }
+        if second != nil {
+            current.Next = &ListNode{second.Val, nil}
+            current = current.Next
+            second = second.Next
+        }
+    }
+    head.Next = newHead.Next.Next
+}
+
+func findMid(head *ListNode) *ListNode {
+    slow, fast := head, head.Next
+    for slow.Next != nil && fast.Next != nil && fast.Next.Next != nil {
+        slow = slow.Next
+        fast = fast.Next.Next
+    }
+    return slow
+}
+
+func reverseList(head *ListNode) *ListNode {
+    newHead := head
+    for head.Next != nil {
+        next := head.Next
+        head.Next = next.Next
+        next.Next = newHead
+        newHead = next
+    }
+    return newHead
+}
+```
+
+## 结语
+
+如果你同我一样热爱数据结构、算法、LeetCode，可以关注我 GitHub 上的 LeetCode 题解：[awesome-golang-leetcode][me]
+
+[title]: https://leetcode.com/problems/reorder-list/
+[me]: https://github.com/kylesliu/awesome-golang-leetcode

src/0143.Reorder-List/Solution.go

@@ -0,0 +1,46 @@
+package Solution
+
+func Solution(head *ListNode) {
+	if nil == head || nil == head.Next {
+		return
+	}
+	mid := findMid(head)
+	first, second := head, reverseList(mid.Next)
+	mid.Next = nil
+
+	newHead := new(ListNode)
+	current := newHead
+	for first != nil || second != nil {
+		if first != nil {
+			current.Next = &ListNode{first.Val, nil}
+			current = current.Next
+			first = first.Next
+		}
+		if second != nil {
+			current.Next = &ListNode{second.Val, nil}
+			current = current.Next
+			second = second.Next
+		}
+	}
+	head.Next = newHead.Next.Next
+}
+
+func findMid(head *ListNode) *ListNode {
+	slow, fast := head, head.Next
+	for slow != nil && fast != nil && fast.Next != nil {
+		slow = slow.Next
+		fast = fast.Next.Next
+	}
+	return slow
+}
+
+func reverseList(head *ListNode) *ListNode {
+	newHead := head
+	for head.Next != nil {
+		next := head.Next
+		head.Next = next.Next
+		next.Next = newHead
+		newHead = next
+	}
+	return newHead
+}

src/0143.Reorder-List/Solution_test.go

@@ -0,0 +1,36 @@
+package Solution
+
+import "testing"
+
+func TestSolution(t *testing.T) {
+	// 测试用例
+	cases := []struct {
+		name string
+		inputs []int
+		expect *ListNode
+	} {
+		{
+			"TestCase 1",
+			[]int{1,2,3,4},
+			UnmarshalListBySlice([]int{1,4,2,3}),
+		},
+		{
+			"TestCase 2",
+			[]int{1,2,3,4,5},
+			UnmarshalListBySlice([]int{1,5,2,4,3}),
+		},
+	}
+
+	// 开始测试
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			linkedList := UnmarshalListBySlice(c.inputs)
+			Solution(linkedList)
+			if !isEqual(linkedList, c.expect) {
+				PrintList(linkedList)
+				PrintList(c.expect)
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v", c.expect, linkedList, c.inputs)
+			}
+		})
+	}
+}