public ListNodeClass MergeKLists(ListNodeClass[] lists)
{
ListNodeClass head = new ListNodeClass(0);
ListNodeClass p = head;
ListNodeClass pMin = null;
bool end = false;
int length = lists.Length;
int index = 0;
while (!end)
{
pMin = new ListNodeClass(int.MaxValue);
end = true;
for (int i = 0; i < length; i++)
{
if (lists[i] != null && pMin.val >= lists[i].val)
{
pMin = lists[i];
index = i;
end = false;
}
}
if (!end)
{
p.next = pMin;
p = p.next;
lists[index] = lists[index].next;
}
}
return(head.next);
}
private ListNodeClass Reverse(ListNodeClass p, int k)
{
int counter = 0;
ListNodeClass[] tmps = new ListNodeClass[k];
ListNodeClass pHead = p;
while (p != null)
{
tmps[counter] = p;
counter++;
p = p.next;
if (counter == k)
{
break;
}
}
if (counter < k)
{
return(pHead);
}
for (int i = k - 1; i > 0; i--)
{
tmps[i].next = tmps[i - 1];
}
tmps[0].next = Reverse(p, k);
return(tmps[k - 1]);
}
/// <summary>
/// 给定一个链表，返回一个list，使得所有小于x的节点，在大于等于x的节点的左边
/// </summary>
/// <param name="head"></param>
/// <param name="x"></param>
/// <returns></returns>
public ListNodeClass Partition(ListNodeClass head, int x)
{
ListNodeClass headL = new ListNodeClass(0);
ListNodeClass headGE = new ListNodeClass(0);
ListNodeClass pL = headL;
ListNodeClass pGE = headGE;
if (head == null || head.next == null)
{
return(head);
}
while (head != null)
{
if (head.val < x)
{
pL.next = head;
pL = pL.next;
}
else
{
pGE.next = head;
pGE = pGE.next;
}
head = head.next;
}
pL.next = headGE.next;
pGE.next = null;
return(headL.next);
}
/// <summary>
/// 给定一个升序链表，返回它所对应的深度平衡BST
/// </summary>
/// <param name="head"></param>
/// <returns></returns>
public TreeNode SortedListToBST(ListNodeClass head)
{
TreeNode res = null;
//快慢指针：一个指针跳一格，另一个指针跳两格，选取中间项，时间复杂度为n^2，空间复杂度为1
//考虑遍历两遍，形成一个数组方便随机访问，时间复杂度为n，空间复杂度为n
if (head == null)
{
return(null);
}
int counter = 0;
ListNodeClass p = head;
while (p != null)
{
counter++;
p = p.next;
}
int[] nums = new int[counter];
counter = 0;
p = head;
while (p != null)
{
nums[counter++] = p.val;
p = p.next;
}
res = DoRecursionBySortedArrayToBST(nums, 0, counter - 1);
return(res);
}
public ListNodeClass ReverseKGroup(ListNodeClass head, int k)
{
if (head == null)
{
return(null);
}
head = Reverse(head, k);
return(head);
}
private ListNodeClass MergeTwoLists2(ListNodeClass l1, ListNodeClass l2)
{
if (l1 == null && l2 == null)
{
return(null);
}
if (l1 == null && l2 != null)
{
return(l2);
}
if (l1 != null && l2 == null)
{
return(l1);
}
var head = new ListNodeClass(0);
var temp = head;
var p1 = l1;
var p2 = l2;
while (true)
{
if (p1 == null)
{
temp.next = p2;
break;
}
if (p2 == null)
{
temp.next = p1;
break;
}
if (p1.val < p2.val)
{
temp.next = p1;
temp = temp.next;
p1 = p1.next;
}
else
{
temp.next = p2;
temp = temp.next;
p2 = p2.next;
}
}
return(head.next);
}
public ListNodeClass RemoveNthFromEnd(ListNodeClass head, int n)
{
ListNodeClass p = head;
ListNodeClass pTarget = null;
ListNodeClass pPre = null;
int counter = 0;
while (p.next != null)
{
counter++;
if (counter == n + 1)
{
pPre = head;
}
if (counter == n)
{
pTarget = head;
}
if (pPre != null)
{
pPre = pPre.next;
}
if (pTarget != null)
{
pTarget = pTarget.next;
}
p = p.next;
}
if (pPre != null && pTarget != null)
{
pPre.next = pTarget.next;
}
else if (pPre == null && pTarget != null)
{
head.next = head.next.next;
}
else if (pPre == null && pTarget == null && counter == 0)
{
return(null);
}
else if (pPre == null && pTarget == null)
{
head = head.next;
}
return(head);
}
public ListNodeClass MergeTwoLists(ListNodeClass l1, ListNodeClass l2)
{
if (l1 == null && l2 != null)
{
return(l2);
}
else if (l1 != null && l2 == null)
{
return(l1);
}
else if (l1 == null && l2 == null)
{
return(null);
}
ListNodeClass head = null;
ListNodeClass p = null;
head = l1.val <= l2.val ? l1 : l2;
l1 = l1 == head ? l1.next : l1;
l2 = l2 == head ? l2.next : l2;
p = head;
while (l1 != null && l2 != null)
{
if (l1.val <= l2.val)
{
p.next = l1;
l1 = l1.next;
}
else
{
p.next = l2;
l2 = l2.next;
}
p = p.next;
}
if (l2 == null)
{
p.next = l1;
}
else if (l1 == null)
{
p.next = l2;
}
return(head);
}
/// <summary>
/// 给定一个链表和两个数字，翻转介于这两个数字之间的数值
/// 申明两个头结点用于存储传入的head和逆向拼接的head，为了应对头转换
/// 存储p1位起始位置前一个元素，p2为逆向拼接的尾元素，最后拼接p1、逆向链表和结束位置的迭代p即可
/// </summary>
/// <param name="head"></param>
/// <param name="m"></param>
/// <param name="n"></param>
/// <returns></returns>
public ListNodeClass ReverseBetween(ListNodeClass head, int m, int n)
{
if (head == null)
{
return(head);
}
int counter = 0;
ListNodeClass headtmp = new ListNodeClass(0);
headtmp.next = head;
head = headtmp;
m++;
n++;
ListNodeClass p = head;
ListNodeClass head2 = new ListNodeClass(0);
ListNodeClass p1 = null;
ListNodeClass p2 = null;
ListNodeClass tmp = null;
while (counter < n && p != null)
{
counter++;
if (counter == m - 1)
{
p1 = p;
}
if (counter == m)
{
p2 = p;
}
if (counter >= m)
{
tmp = head2.next;
head2.next = p;
p = p.next;
head2.next.next = tmp;
continue;
}
p = p.next;
}
p1.next = head2.next;
p2.next = p;
return(head.next);
}
public ListNodeClass SwapPairs(ListNodeClass head)
{
ListNodeClass resHead = null;
ListNodeClass p1 = null;
ListNodeClass p2 = null;
ListNodeClass p = null;
//for the first
p1 = head;
if (p1 == null)
{
return(null);
}
p2 = p1.next;
if (p2 == null)
{
return(head);
}
resHead = p2;
p1.next = p2.next;
p2.next = p1;
p = p1;
//for loop
while (true)
{
if (p1.next == null)
{
break;
}
p1 = p1.next;
if (p1.next == null)
{
break;
}
p2 = p1.next;
p1.next = p2.next;
p2.next = p1;
p.next = p2;
p = p1;
}
return(resHead);
}
//almost the same speed as mine
public ListNodeClass BestSolution(ListNodeClass head)
{
if (head != null && head.next != null)
{
ListNodeClass nextHead = head.next.next;
var temp = head;
head = head.next;
head.next = temp;
if (nextHead != null)
{
temp.next = SwapPairs(nextHead);
}
else
{
temp.next = null;
}
}
return(head);
}
public ListNodeClass RotateRight(ListNodeClass head, int k)
{
if (head == null || head.next == null)
{
return(head);
}
int counter = 1;
ListNodeClass p = head;
ListNodeClass tail = null;
ListNodeClass tail_pre = null;
p = head;
while (p.next != null)
{
tail_pre = p;
p = p.next;
counter++;
}
counter = k % counter;
for (int i = 0; i < counter; i++)
{
tail = p;
tail.next = head;
head = tail;
tail_pre.next = null;
if (i == counter - 1)
{
break;
}
else
{
p = head;
while (p.next != null)
{
tail_pre = p;
p = p.next;
}
}
}
return(head);
}