92. Reverse Linked List II
在链表头添加一个虚拟源点,可以减少特判
/*** Definition for singly-linked list.* struct ListNode {* int val;* ListNode *next;* ListNode() : val(0), next(nullptr) {}* ListNode(int x) : val(x), next(nullptr) {}* ListNode(int x, ListNode *next) : val(x), next(next) {}* };*/
class Solution {
public:ListNode* reverseBetween(ListNode* head, int left, int right) {if(right == left) {return head;}int cnt = 1;ListNode* cur = head;ListNode* prev = new ListNode(0, head), *next = nullptr, *vir = prev;while(cnt < left) {cnt++;prev = cur;cur = cur->next;}ListNode *L = prev, *L1 = cur;while(cnt <= right) {cnt++;if(cnt == right) {L->next = cur->next;}next = cur->next;cur->next = prev;prev = cur;cur = next;}if(cur)L1->next = cur;else L1->next = nullptr;return vir->next;}
};