【LeetCode】92. Reverse Linked List II

1.题目描述

Reverse a linked list from position m to n. Do it in one-pass.

反转从位置 m 到 n 的链表。请使用一趟扫描完成反转。

Note: 1 ≤ m ≤ n ≤ length of list.

Example:

Input: 1->2->3->4->5->NULL, m = 2, n = 4
Output: 1->4->3->2->5->NULL

2.Solutions

public static ListNode reverseBetween(ListNode head, int m, int n) {
    ListNode dummy = new ListNode(0);
    dummy.next = head;
    //first part
    ListNode cur1 = dummy;
    ListNode pre1 = null;
    for(int i=0;i<m;i++){
        pre1 = cur1;
        cur1 = cur1.next;
    }

    //reverse
    ListNode cur2 = cur1;
    ListNode pre2 = pre1;
    ListNode next;
    for(int i=m;i<=n;i++){
        next = cur2.next;
        cur2.next = pre2;
        pre2 = cur2;
        cur2 = next;
    }

    //connect 
    pre1.next = pre2;
    cur1.next = cur2;

    return dummy.next;
}

参考：【链表】打卡2：如何优雅着反转单链表

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