0092Reverse_Linked_List_II.cpp

/**
 * 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) {
        ListNode *l, *r;
        while(left<=right){
            l=r=head;
            for(int i=0; i<left-1; i++){
                l=l->next;
            }
            for(int i=0; i<right-1; i++){
                r=r->next;
            }
            swap(l->val, r->val);
            left++;
            right--;
        }
        return head;
    }
};