Linked List--flips the node position of a single linked list from M to n

Title: Reverse list of nodes from m-n locations

For example:
Given1->2->3->4->5->null, m = 2 and n = 4,

Return1->4->3->2->5->null.

The nodes from the second to the fourth are reversed.

where m and n satisfy the condition:
1≤ m ≤ N ≤length of the list.

Ideas:

Still in reverse order, consider using a secondary space stack.

The nodes of the m-n are sequentially placed into the stack and marked with the front and back two nodes adjacent to the stack node Pfirst and Psecond.

(if m==1,pfirst=null, regardless of whether n is the length of the list, there is no effect on the psecond situation.) )

The code is as follows:

/** * Definition for singly-linked list. * public class ListNode {* int val; * ListNode Next; * ListNode (int x) {* val = x; * Next = Null        *} *} */import java.util.*;p Ublic class Solution {public ListNode Reversebetween (listnode head, int m, int n) {        if (head==null) return null;                if (m==n) return head;        stack<listnode> stack=new Stack ();                The nodes of the m-n are put into the stack, and the two nodes adjacent to each other are marked;                int num=1;        ListNode Pfirst=null;                ListNode Psecond=null;        ListNode P=head;        Special cases, when m==1, the head node changes;            if (m==1) {pfirst=null;             } for (; num<=n;num++) {//record pfirst;                if (num<m) {if (num==m-1) {pfirst=p;                  } P=p.next; } else if (NUM&GT;=M&AMp;&num<=n) {Stack.push (P);            P=p.next;               }}//The general condition of recording Psecond,psecond still applies to the special case of n=length of list;                Psecond=p;        Start the operation of the linked list;            if (pfirst==null) {head=stack.pop ();        Pfirst=head;            } while (!stack.empty ()) {Pfirst.next=stack.pop ();        Pfirst=pfirst.next;        } Pfirst.next=psecond;    return head; }}

Linked List--flips the node position of a single linked list from M to n