LeetCode/com/zerroi/leetcode/Three24/ReverseBetween.java

package com.zerroi.leetcode.Three24;

public class ReverseBetween {
    public static void main(String[] args) {

    }
}

class ListNode {
    int val;
    ListNode next;
    ListNode() {}
    ListNode(int val) { this.val = val; }
    ListNode(int val, ListNode next) { this.val = val; this.next = next; }
}

class Solution {
    public ListNode reverseBetween(ListNode head, int left, int right) {
        if (left == right) return head;
        ListNode dummy1 = new ListNode(-1);
        ListNode dummy2 = new ListNode(-1);
        ListNode cur1 = dummy1;
        ListNode cur2 = dummy2;
        for (int i = 0; i < left - 1; i++) {
            cur1.next = new ListNode(head.val);
            cur1 = cur1.next;
            head = head.next;
        }
        for (int i = left; i <= right; i++) {
            cur2.next = new ListNode(head.val);
            cur2 = cur2.next;
            head = head.next;
        }
        ListNode reversed = reverse(dummy2.next);
        cur1.next = reversed;
        cur2.next = head;
        return dummy1.next;

    }
    private ListNode reverse(ListNode head) {
        ListNode pre = null;
        ListNode cur = head;
        ListNode temp;
        while (cur != null) {
            temp = cur.next;
            cur.next = pre;
            pre = cur;
            cur = temp;
        }
        return pre;
    }
}