private ListNode mergeSort(ListNode head, ListNode tail)
{
if (head.next == tail)
{ //single node
head.next = null;
return head;
}
ListNode itr = head, mid = head;
while (itr != tail)
{
itr = itr.next;
if (itr != tail)
{
itr = itr.next;
}
mid = mid.next;
}
ListNode l1 = mergeSort(head, mid);
ListNode l2 = mergeSort(mid, tail);
return MergeListNode(l1, l2);
}
/// <summary>
///
/// </summary>
/// <param name="head"></param>
public static void ReorderList(ListNode head)
{
if (head == null || head.next == null) return;
var reMidNode = FindMid(head);
reMidNode = ReverseList(reMidNode);
var beginNode = head;
var tempNode = head;
while (reMidNode != null)
{
tempNode = tempNode.next;
beginNode.next = reMidNode;
reMidNode = reMidNode.next;
beginNode = beginNode.next;
beginNode.next = tempNode;
beginNode = beginNode.next;
}
beginNode.next = null;
}
public static ListNode DeleteDuplicates(ListNode head)
{
if (head == null || head.next == null)
{
return head;
}
ListNode Cur = head;
ListNode Perv = head.next;
while (Perv != null)
{
if (Perv.val == Cur.val)
{
Cur.next = Perv.next;
Perv = Perv.next;
}
else
{
Cur = Cur.next;
Perv = Perv.next;
}
}
return head;
}
public static ListNode ReverseList(ListNode head, int m, int n)
{
if (head == null || m == n)
{
return head;
}
ListNode tempHead = new ListNode(0);
tempHead.next = head;
var mNode = tempHead;
ListNode current, pnext;
int i = 1;
while (i < m)
{
mNode = mNode.next;
i++;
}
current = mNode.next;
while (current.next != null && i < n)
{
pnext = current.next;
current.next = pnext.next;
pnext.next = mNode.next;
mNode.next = pnext;
i++;
}
return tempHead.next;
}
public ListNode SortList(ListNode head)
{
if (head == null) //trap
return null;
return mergeSort(head, null);
}
public ListNode SwapPairs(ListNode head)
{
ListNode tempHead = new ListNode(-1);
tempHead.next = head;
var node = tempHead;
ListNode current, pnext;
current = node.next;
while (current != null)
{
pnext = current.next;
if (pnext != null)
{
//交换
current.next = pnext.next;
pnext.next = node.next;
node.next = pnext;
//重置
node = current;
current = node.next;
}
else
{
break;
}
}
return tempHead.next;
}
/// <summary>
/// 反转一个链表
/// </summary>
public static void Test()
{
ListNode l1 = new ListNode(2);
ListNode l2 = new ListNode(3);
ListNode l3 = new ListNode(4);
l2.next = l3;
l1.next = l2;
var node = ReverseList(l1);
}
/// <summary>
/// 时间复杂度要求要nlogn ，空间要求不开辟新的内存空间，
/// 选择用归并排序来做
/// </summary>
public static void Test()
{
ListNode l1 = new ListNode(2);
ListNode l2 = new ListNode(3);
ListNode l3 = new ListNode(1);
ListNode l4 = new ListNode(4);
l2.next = l3;
l1.next = l2;
var list = new Sort_List().SortList(l1);
}
public static void Test()
{
ListNode l1 = new ListNode(1);
ListNode l2 = new ListNode(2);
ListNode l3 = new ListNode(10);
ListNode l4 = new ListNode(2);
ListNode l5 = new ListNode(1);
//l4.next = l5;
//l3.next = l4;
//l2.next = l3;
l1.next = l2;
Console.Write(IsPalindrome(l1));
}
/// <summary>
/// 找到中间列表
/// </summary>
/// <param name="head"></param>
/// <returns></returns>
protected static ListNode FindMid(ListNode head)
{
var beginNode = head;
var midNode = head;
while (beginNode != null)
{
beginNode = beginNode.next;
midNode = midNode.next;
if (beginNode != null)
{
beginNode = beginNode.next;
}
}
return midNode;
}
/// <summary>
/// </summary>
public static void Test()
{
ListNode l1 = new ListNode(2);
ListNode l2 = new ListNode(3);
ListNode l3 = new ListNode(4);
l2.next = l3;
l1.next = l2;
var node = RemoveNthFromEnd(l1, 4);
while (node != null)
{
Console.WriteLine(node.val);
node = node.next;
}
}
public static void Test()
{
ListNode head = new ListNode(1);
var tempHead = head;
for (int i = 2; i < 4; i++)
{
ListNode temp = new ListNode(i);
tempHead.next = temp;
tempHead = tempHead.next;
}
ReorderList(head);
while (head != null)
{
Console.WriteLine(head.val);
head = head.next;
}
}
public static ListNode RemoveNthFromEnd(ListNode head, int n)
{
if (head == null)
{
return null;
}
if (n == 0)
{
return head;
}
ListNode tempHead = new ListNode(0);
tempHead.next = head;
ListNode current;
current = tempHead.next;
int totel = 0;
while (current != null)
{
current = current.next;
totel++;
}
int number = totel - n;
current = tempHead;
while (current != null)
{
if (number == 0)
{
if (current.next != null)
{
current.next = current.next.next;
}
}
current = current.next;
number--;
}
return tempHead.next;
}
public static void Test()
{
ListNode x = new ListNode(1);
ListNode x1 = new ListNode(1);
ListNode x2 = new ListNode(2);
ListNode x3 = new ListNode(3);
x2.next = x3;
x1.next = x2;
x.next = x1;
var head = DeleteDuplicates(x);
while (head != null)
{
Console.WriteLine(head.val);
head = head.next;
}
}
public static void Test()
{
ListNode head = new ListNode(1);
var tempHead = head;
for (int i = 2; i < 9; i++)
{
ListNode temp = new ListNode(i);
tempHead.next = temp;
tempHead = tempHead.next;
}
var list = OddEvenList(head);
while (list != null)
{
Console.WriteLine(list.val);
list = list.next;
}
}
public static ListNode MergeKLists(ListNode[] lists)
{
if (lists == null || lists.Count() == 0)
return null;
if (lists.Count() == 1)
{
return lists[0];
}
List<int> numbers = new List<int>();
foreach (var list in lists)
{
var tempList = list;
int middle = numbers.Count();
while (tempList != null)
{
numbers.Add(tempList.val);
tempList = tempList.next;
}
if (numbers.Count() > 0 && middle != numbers.Count())
{
//两两归并
Merge(numbers, 0, middle, numbers.Count());
}
}
if (numbers.Count() > 0)
{
ListNode node = new ListNode(numbers[0]);
ListNode head = node;
int i = 1;
while (i < numbers.Count)
{
node.next = new ListNode(numbers[i]);
node = node.next;
i++;
}
return head;
}
else
return null;
}
public static ListNode DeleteDuplicates(ListNode head)
{
if (head == null || head.next == null)
{
return head;
}
ListNode temp = new ListNode(int.MinValue);
temp.next = head;
ListNode Cur = temp;
ListNode Next = temp.next;
ListNode Pre = temp;
while (Next != null)
{
if (Next.val == Cur.val)
{
Next = Next.next;
while (Next != null && Next.val == Cur.val)
{
Next = Next.next;
}
Pre.next = Next;
Cur = Pre.next;
if (Next == null)
{
return temp.next;
}
Next = Next.next;
}
else
{
Pre = Cur;
Cur = Cur.next;
Next = Next.next;
}
}
return temp.next;
}
public static void Test()
{
ListNode l1 = new ListNode(1);
ListNode l2 = new ListNode(2);
ListNode l3 = new ListNode(3);
ListNode l4 = new ListNode(4);
l3.next = l4;
l2.next = l3;
l1.next = l2;
DeleteNode(l1);
var temp = l1;
while (temp != null)
{
Console.WriteLine(temp.val);
temp = temp.next;
}
}
/// <summary>
/// 反转一个链表
/// </summary>
public static void Test()
{
ListNode l1 = new ListNode(2);
ListNode l2 = new ListNode(3);
ListNode l3 = new ListNode(4);
ListNode l4 = new ListNode(5);
l3.next = l4;
l2.next = l3;
l1.next = l2;
var node = ReverseList(l1, 2, 3);
while (node != null)
{
Console.WriteLine(node.val);
node = node.next;
}
}
public static void Test()
{
ListNode l1 = new ListNode(1);
ListNode l2 = new ListNode(2);
ListNode l3 = new ListNode(3);
ListNode l4 = new ListNode(4);
ListNode l5 = new ListNode(5);
l4.next = l5;
l3.next = l4;
l2.next = l3;
l1.next = l2;
var node = new Swap_Nodes_in_Pairs().SwapPairs(l1);
while (node != null)
{
Console.WriteLine(node.val);
node = node.next;
}
}
public static ListNode OddEvenList(ListNode head)
{
if (head == null || head.next == null || head.next.next == null) return head;
var odd = head;
var oddHead = odd;
var even = head.next;
var evenHead = even;
while (even != null && even.next != null)
{
//奇数的下一个连接偶数的下一个
odd.next = even.next;
odd = odd.next;
even.next = odd.next;
even = even.next;
}
odd.next = evenHead;
return oddHead;
}
public static ListNode ReverseList(ListNode head)
{
if(head==null)
{
return null;
}
ListNode tempHead = new ListNode(0);
tempHead.next = head;
ListNode current, pnext;
current = tempHead.next;
while (current.next != null)
{
pnext = current.next;
current.next = pnext.next;
pnext.next = tempHead.next;
tempHead.next = pnext;
}
return tempHead.next;
}
public ListNode MergeListNode(ListNode first, ListNode secend)
{
ListNode MergeListNode = new ListNode(-1);
ListNode MergeListNodehead = MergeListNode;
//相邻两组开始归并（每组都已排序）
while (first != null && secend != null)
{
if (first.val > secend.val)
{
MergeListNode.next = secend;
secend = secend.next;
MergeListNode = MergeListNode.next;
}
else
{
MergeListNode.next = first;
first = first.next;
MergeListNode = MergeListNode.next;
}
}
//把两组中剩余的值加入到列表中
if (first != null)
{
MergeListNode.next = first;
}
if (secend != null)
{
MergeListNode.next = secend;
}
return MergeListNodehead.next;
}
/// <summary>
/// 思路：把中间后半段的链表反转，然后进行比较
/// </summary>
/// <param name="head"></param>
/// <returns></returns>
public static bool IsPalindrome(ListNode head)
{
if (head == null || head.next == null)
{
return true;
}
var begin = head;
var mid = FindMid(head);
mid = ReverseList(mid);
while (mid != null)
{
if (begin.val != mid.val)
{
return false;
}
begin = begin.next;
mid = mid.next;
}
return true;
}
static void Add_Two_NumbersMain()
{
ListNode l1 = new ListNode(9);
ListNode l2 = new ListNode(9);
ListNode l3 = new ListNode(3);
//l2.next = l3;
l1.next = l2;
ListNode m1 = new ListNode(9);
ListNode m2 = new ListNode(6);
ListNode m3 = new ListNode(4);
//m2.next = m3;
//m1.next = m2;
int[] numbers = { -1, -2, -3, -4, -5 };
var nodes = Add_Two_Numbers.AddTwoNumbers(l1, m1);
Console.WriteLine(nodes.ToString());
}
/// <summary>
/// 明白题目的意思就很好做了
/// </summary>
/// <param name="node"></param>
public static void DeleteNode(ListNode node)
{
node.val = node.next.val;
node.next = node.next.next;
}
public static void Test()
{
ListNode l1 = new ListNode(2);
ListNode l2 = new ListNode(3);
ListNode l3 = new ListNode(4);
l2.next = l3;
l1.next = l2;
ListNode n1 = new ListNode(4);
ListNode n2 = new ListNode(5);
ListNode n3 = new ListNode(6);
n2.next = n3;
n1.next = n2;
//ListNode[] lists = new ListNode[] { n1, l1 };
ListNode[] lists = new ListNode[] { l1, null, n1 };
var node = MergeKLists1(lists);
}
public static ListNode MergeKLists1(ListNode[] lists)
{
if (lists == null || lists.Count() == 0)
return null;
if (lists.Count() == 1)
{
return lists[0];
}
ListNode node = new ListNode(-1);
ListNode head = node;
node.next = lists[0];
for (int i = 1; i < lists.Count(); i++)
{
if (lists[i] != null)
{
node.next = MergeListNode(node.next, lists[i]);
}
}
return head.next;
}
public static ListNode AddTwoNumbers(ListNode l1, ListNode l2)
{
var l3 = new ListNode(0);
if (l1 == null && l2 == null)
{
return null;
}
else if (l1 == null)
{
l3.val = l2.val;
ListNode copyl2 = l2.next;
l3.next = AddTwoNumbers(null, copyl2);
}
else if (l2 == null)
{
ListNode copyl1 = l1.next;
if (l1.val >= 10)
{
l3.val = l1.val - 10;
if (copyl1 != null)
{
copyl1.val += 1;
}
else
{
copyl1 = new ListNode(1);
}
}
else
{
l3.val = l1.val;
}
l3.next = AddTwoNumbers(copyl1, null);
}
else
{
int sum = l2.val + l1.val;
ListNode copyl1 = l1.next;
if (sum >= 10)
{
sum = sum - 10;
if (copyl1 != null)
{
copyl1.val += 1;
}
else
{
copyl1 = new ListNode(1);
}
}
l3.val = sum;
l3.next = AddTwoNumbers(copyl1, l2.next);
}
return l3;
}
/// <summary>
/// 反转列表
/// </summary>
/// <param name="head"></param>
/// <returns></returns>
protected static ListNode ReverseList(ListNode node)
{
ListNode head = new ListNode(0);
head.next = node;
ListNode current, pnext;
current = head.next;
while (current.next != null)
{
pnext = current.next;
current.next = pnext.next;
pnext.next = head.next;
head.next = pnext;
}
return head.next;
}