LeetCode 92. Reverse Linked List II

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class Solution {
public:
    ListNode* reverseBetween(ListNode* head, int left, int right) {
        if (left == right) return head;
        ListNode* dummyHead = new ListNode(0, head);
        ListNode* prev = dummyHead;
        int i = 1;
        for (; i < left; ++i)
            prev = prev->next;
        ListNode *conn = prev, *tail = prev->next ,*curr = prev->next;
        while (i++ <= right) {
            ListNode* next = curr->next;
            curr->next = prev;
            prev = curr;
            curr = next;
        }
        if (conn) conn->next = prev;
        else dummyHead->next = prev;
        tail->next = curr;
        return dummyHead->next;
    }
};
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class Solution {
public:
    ListNode* reverseBetween(ListNode* head, int left, int right) {
        if (left == right) return head;
        ListNode* dummyHead = new ListNode(0, head);
        ListNode* prev = dummyHead;
        int i = 1;
        for (; i < left; ++i)
            prev = prev->next;
        ListNode *curr = prev->next, *next;
        while (i++ < right) {
            next = curr->next;
            curr->next = next->next;
            next->next = prev->next;
            prev->next = next;
        }
        return dummyHead->next;
    }
};