LeetCode 92: Reverse Linked List II Solution

Master LeetCode problem 92 (Reverse Linked List II), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

92. Reverse Linked List II

Problem Explanation

Explanation:

To solve this problem, we can follow these steps:

  1. Traverse the linked list until we reach the left-th node.
  2. Reverse the nodes from left to right by changing the pointers accordingly.
  3. Reconnect the reversed sublist back to the original list.
  4. Return the modified linked list.

Time complexity: O(n) - we only traverse the list once Space complexity: O(1) - we use constant extra space

:

Solution Code

class Solution {
    public ListNode reverseBetween(ListNode head, int left, int right) {
        if (head == null) return null;
        
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode pre = dummy;
        
        for (int i = 0; i < left - 1; i++) {
            pre = pre.next;
        }
        
        ListNode start = pre.next;
        ListNode then = start.next;
        
        for (int i = 0; i < right - left; i++) {
            start.next = then.next;
            then.next = pre.next;
            pre.next = then;
            then = start.next;
        }
        
        return dummy.next;
    }
}

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