Remove Duplicates from Sorted List && Merge Two Sorted Lists && Linked List Cycle && Remove Nth Node

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Remove Duplicates from Sorted List

1、已排序的链表删除相同的数据。

    ListNode *deleteDuplicates(ListNode *head) {        ListNode *p = head;        int temp;                while (p != NULL) {            temp = p->val;            ListNode *q = p->next;            if (q != NULL && q->val == temp) {                p->next = q->next;                free(q);            }            else                 p = p->next;        }        return head;    }

Merge Two Sorted Lists

1、合并两个链表

    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {        if (l1 == NULL)            return l2;        else if (l2 == NULL)            return l1;        ListNode *head;        if (l1->val < l2->val) {    head = l1;    l1 = l1->next;    }    else {        head = l2;        l2 = l2->next;    }    ListNode *p = head;        while (l1 != NULL || l2 != NULL) {            if (l1 != NULL && (l2 == NULL || l1->val < l2->val)) {                p->next = l1;p = p->next;l1 = l1->next;            }else {                p->next = l2;p = p->next;l2 = l2->next;            }    }    p->next = NULL;    return head;    }

2、这里也可以用递归的方法，代码会简洁很多。

Linked List Cycle

1、两个指针相差一的步进长度，往前走，如果相遇那么就是有环。

    bool hasCycle(ListNode *head) {        if (head == NULL || head->next == NULL)            return false;        ListNode *p, *q;        p = q = head;        while (1) {            p = p->next;            q = q->next->next;            if (p == NULL || q == NULL || q->next == NULL)                return false;            if (p == q)                return true;        }    }

Swap Nodes in Pairs

1、交换链表中前后两个数据节点。

    ListNode *swapPairs(ListNode *head) {        if (head == NULL || head->next == NULL)            return head;        ListNode *p = head;        ListNode *q = head->next->next;        head = p->next;        p->next->next = p;        p->next = q;        ListNode *temp;        while (q != NULL && q->next != NULL) {            p->next = q->next;            p = p->next;            temp = q;            q = q->next->next;            p->next = temp;            p = p->next;        }        p->next = q;        return head;    }

Linked List Cycle II

1、这里利用上面Linked List Cycle的函数，找到相遇点。

</pre><pre name="code" class="cpp">class Solution {public:    ListNode *detectCycle(ListNode *head) {        ListNode *p = findMeetPoint(head);        if (p != NULL) {            ListNode *q = head;            while (q != p) {                q = q->next;                p = p->next;            }            return q;        }        else            return NULL;    }private:    ListNode *findMeetPoint(ListNode *head) {        if (head == NULL || head->next == NULL)            return NULL;        ListNode *p, *q;        p = q = head;        while (1) {            p = p->next;            q = (q->next)->next;            if (p == NULL || q == NULL || q->next == NULL)                return NULL;            if (p == q)                return p;        }    }};

Remove Nth Node From End of List

1、两个指针，第一个先移动n个点。然后后面的指针就是要删除的点。

    ListNode *removeNthFromEnd(ListNode *head, int n) {        ListNode *pre = head, *end = head;        while (n--)             end = end->next;             if (end == NULL) {            head = head->next;            free(pre);            return head;        }        while (end->next != NULL) {            pre = pre->next;            end = end->next;        }        ListNode *temp = pre->next;        pre->next = temp->next;        free(temp);        return head;    }

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