题解 | #链表内指定区间反转#

import java.util.*;

/*

• public class ListNode {
• int val;
• ListNode next = null;
• } */

public class Solution { /** * * @param head ListNode类 * @param m int整型 * @param n int整型 * @return ListNode类 */ public ListNode reverseBetween (ListNode head, int m, int n) { // write code here

    if(head == null){
        return null;
    }
    if(head.next==null || m==n){
        return head;
    }
    
    ListNode startNode1 = null;
    ListNode startNode2 = null;
    ListNode endNode1 = null;
    ListNode endNode2 = null;
    ListNode copyHead = head;
    ListNode copyHead2 = head;
    
    if(m==1){
        startNode1=startNode2 = head;
        for(int i=1;i<n;i++){
            head = head.next;
        }
        endNode1 = head;
        endNode2 = head.next;
        endNode1.next = null;
        ListNode reverseList=null;
        reverseList = ReverseList(startNode1);
        copyHead = reverseList;
        while(reverseList.next!=null){
            reverseList = reverseList.next;
        }
        reverseList.next = endNode2;
        return copyHead;
    }else{
        for(int i=1;i<m-1;i++){
            head = head.next;
        }
        startNode1 = head;
        startNode2 = head.next;
        startNode1.next=null;
        head = startNode2;
        
        
        for(int i=m;i<n;i++){
            head = head.next;
        }
        endNode1 = head;
        endNode2 = head.next;
        endNode1.next = null;
        ListNode reverseList=null;
        
        reverseList=ReverseList(startNode2);
        ListNode end = reverseList;
        while(end.next!=null){
            end = end.next;
        }
        startNode1.next=reverseList;
        end.next = endNode2;
        return copyHead;
    } 
}

public ListNode ReverseList(ListNode head) {
    if(head==null){
        return null;
    }
    ListNode currentNode = null;
    ListNode temp = null;
    ListNode endNode = null;
    if(head.next==null){
        return head;
    }else{
        currentNode = head.next;
        head.next = null;
        endNode = head;
    }
    while(currentNode!=null){
        temp = currentNode.next;
        currentNode.next = head;
        head = currentNode;
        currentNode = temp;
    }
    return head;
    
}

}