92

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int val=0, ListNode next=null) {
 *         this.val = val;
 *         this.next = next;
 *     }
 * }
 */
public class Solution {
    public ListNode ReverseBetween(ListNode head, int left, int right) {
        var dummy = new ListNode(0, head);
        var prev = dummy;
 
        for (int i = 1; i < left; i++)
            prev = prev.next;                 // prev = node just before the reversal zone
 
        var curr = prev.next;                 // curr = first node of the zone; it ends up as the zone's tail
 
        for (int i = 0; i < right - left; i++) {
            var next = curr.next;             // node to move to the front of the zone
            curr.next = next.next;            // unlink it
            next.next = prev.next;            // point it at the current zone front
            prev.next = next;                 // make it the new zone front
        }
 
        return dummy.next;
    }
}

It’s tricky to implement.