题解 | #链表内指定区间反转#

import java.util.*; 
import java.util.Stack;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @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(m==1) ListNode first = head;
        if(n-m>0){
        ListNode first_pre = head;
        ListNode last = head;
        ListNode first = head;
        //if(m>1){
        for(int i = 1;i<m-1;i++){
            first_pre = first_pre.next;
        }
        if(m>1){first = first_pre.next;}
        //}
        for(int j = 1;j<n;j++){
            last = last.next;
        }
        ListNode last_last = last.next;
        Stack<ListNode> stack = new Stack<>();
        ListNode Shead = first;
        int i = 0;
        while(Shead!=null){
            stack.push(Shead);
            Shead = Shead.next;
            i++;
            if(i == n-m +1) break;
        }
        ListNode node = stack.pop();
        ListNode first2 = node;
        if(m==1) head=first2;
        while(!stack.isEmpty()){
            ListNode temp = stack.pop();
            node.next = temp;
            node = node.next;
        }
        if (m!=1)first_pre.next = first2;
        node.next = last_last;
        }  
        return head;
    
}
}