1，制作环型链表

2。检測链表中是否存在环（參考文章）

3。计算链表中环的长度

4， 计算链表中环起始的位置

5，推断一个链表是否存在回文，要求O（n）时间和O（1）空间的复杂度（推断链表是否是回文，要求O(n)时间。O(1)空间）

6。计算链表中间位置

7，链表原地反转（链表原地反转）

8，測试code

#include <iostream>
using namespace std;
/*@1: detect if there is a circule in a list -> detect_circule_exist@2: calculate the circule length in the list -> give_circ_len@3: locate the place where the circule starts -> locate_circ_place@4: detect if the list is palindrome -> time:o(n) and space:o(1)
*/
/*struct simple linked list
*/
struct item
{int n;struct item *next;
};
class iter {struct item *head;int circ_len;
public:void insert(int i);bool remove(int i);iter(){this->circ_len = 0;this->head = new(struct item);this->head->next = NULL;}bool create_circule(int i);void remove_circule();bool detect_circule_exist();int give_circ_len();int locate_circ_place();bool detect_palindrome();void display();~iter();
};
void iter::insert(int i) {struct item *cur;struct item *add_item = new(struct item);add_item->n = i;add_item->next = NULL;/* insert at tail */cur = this->head;while(cur->next) {cur = cur->next;}cur->next = add_item;cout << add_item <<endl;
}
bool iter::remove(int i)
{struct item *cur = this->head->next, *prev = this->head;while (cur) {if (cur->n == i) {prev->next = cur->next;return true;} else {cur = cur->next;prev = prev->next;}}return false;
}
void iter::display()
{struct item *cur = this->head->next;while (cur){cout << cur->n << " -> ";cur = cur->next;}cout <<"end" << endl;
}/* create a circult at value: i, if not i exist return false*/
bool iter::create_circule(int i)
{struct item *cur = this->head;struct item *find = NULL;while (cur->next){cur = cur->next;if (cur->n == i) {find = cur;}}if (find) {cur->next = find;return true;} elsereturn false;
}
/* detect if exist a circule in the linked list */
bool iter:: detect_circule_exist()
{/*quick and slow point to the first element of the linked list*/struct item *quick, *slow, *mark;bool find = false;slow = this->head->next;quick = this->head->next->next;while (quick && slow) {if (!find) {if (quick == slow) {find = true;mark = slow;slow = slow->next;this->circ_len++;} else {if (!quick->next || !quick->next->next)break;if (!slow->next)break;quick = quick->next->next;slow = slow->next;}} else {if (mark == slow) {return true;} else {slow = slow->next;this->circ_len++;}}}find = false;return find;}
int iter:: give_circ_len()
{this->detect_circule_exist();return this->circ_len;
}
/* cal the len of non circule at the linked list */
int iter:: locate_circ_place()
{if (this->detect_circule_exist()) {struct item *quick, *slow;int i = this->circ_len;slow = this->head->next;quick = this->head->next;while (quick && i--) {quick = quick->next;}i = 0;while (quick && slow) {if (quick == slow) {return i;} else {i++;quick = quick->next;slow = slow->next;}}} else {return 0;}
}
void iter:: remove_circule()
{struct item *tail = this->head;struct item *mark;int i = this->locate_circ_place() + 1;while (tail->next && i--){tail = tail->next;}mark = tail;while (tail) {if (tail->next == mark) {tail->next = NULL;return;} else {tail = tail->next;}}
}
bool iter:: detect_palindrome()
{struct item *quick, *slow;/*first find the middle place of the linked list by quick and slow pointer*/slow = this->head->next;quick = this->head->next->next;while (slow) {struct item *mark;slow = slow->next;quick = quick->next->next;if (!quick) {/*reverse the linked list at the place*/mark = slow;quick = slow->next->next; /*q*/slow = slow->next; /*p*/struct item *temp;while (quick) {temp = quick->next;quick->next = slow;slow = quick;quick = temp;}mark->next->next = NULL;mark->next = slow;slow = this->head->next;mark = mark->next;while (slow && mark) {//cout << "odd first part: "<< slow->n << "addr:"  << slow << "second part: " << mark->n << "addr:" << mark <<endl;if (slow->n != mark->n)return false;else {slow = slow->next;mark = mark->next;}}return true;}if (!quick->next) {/*reverse the linked list at the place*/mark = slow;quick = slow->next->next; /*q*/slow = slow->next; /*p*/struct item *temp;while (quick) {temp = quick->next;quick->next = slow;slow = quick;quick = temp;}mark->next->next = NULL;mark->next = slow;slow = this->head->next;mark = mark->next;while (slow && mark) {//cout << "even first part: "<< slow->n << "addr:"  << slow << "second part: " << mark->n << "addr:" << mark <<endl;if (slow->n != mark->n)return false;else {slow = slow->next;mark = mark->next;}}return true;}}
}
iter::~iter()
{struct item *cur = this->head->next;if (this->detect_circule_exist())this->remove_circule();while (cur){struct item *temp = cur;cur = cur->next;delete temp;//cout <<"delete" << temp<< endl;}delete this->head;}
int main()
{class iter myiter;/*for (int i = 0; i < 10; i++) {myiter.insert(i);}myiter.create_circule(2);if (myiter.detect_circule_exist())cout << "detect circule exist and circ len" << myiter.give_circ_len()<< endl;elsecout << "no detect circule exist" <<endl;cout << "circ point index" << myiter.locate_circ_place() <<endl;myiter.remove_circule();myiter.display();*//*myiter.insert(1);myiter.insert(2);myiter.insert(3);myiter.insert(3);myiter.insert(2);myiter.insert(1);if (myiter.detect_palindrome())cout << "even detect palindrome" <<endl;elsecout << "even no detect palindrome" <<endl;*/myiter.insert(1);myiter.insert(2);myiter.insert(3);myiter.insert(2);myiter.insert(1);if (myiter.detect_palindrome())cout << "odd detect palindrome" <<endl;elsecout << "odd no detect palindrome" <<endl;return 1;
}