[LeetCode] Reverse Linked List II

最新推荐文章于 2022-10-08 18:10:16 发布

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本文介绍了一种算法，用于在单次遍历中就地反转链表的指定区间，从位置m到n。提供了完整的C++实现示例，并讨论了边界条件。

Reverse a linked list from position m to n. Do it in-place and in one-pass.

For example:
Given 1->2->3->4->5->NULL, m = 2 and n = 4,

return 1->4->3->2->5->NULL.

Note:
Given m, n satisfy the following condition:

1 ≤ m ≤ n ≤ length of list.

class Solution {
public:
    ListNode *reverseBetween(ListNode *head, int m, int n) {
        ListNode *dumllHead = new ListNode(-1);
        dumllHead -> next = head;
        ListNode *p = dumllHead;
        ListNode *pfore = dumllHead;
        ListNode *pre = dumllHead;
        ListNode *q = dumllHead;
        ListNode *qback = q -> next;
        int cnt = 0,mm = m,nn = n;
        while(nn){
            if(mm){
                pfore = p;
                p = p -> next;
                mm --;
            }
            pre = q;
            q = qback;
            nn --;
            cnt ++;
            if(cnt > m){
                qback = q -> next;
                q -> next = pre;
            }else
                qback = q -> next;
        }
        pfore -> next = q;
        p -> next = qback;
        return dumllHead -> next;
    }
};