leetcode Top100(23)回文链表

给你一个单链表的头节点 head ，请你判断该链表是否为回文链表。如果是，返回 true ；否则，返回 false 
输入：head = [1,2,2,1]
输出：true

采用动态数组，判断数组对称就可以了（这解法空间复杂度o(n)）

package TOP21_30;
 
import Util.ListNode;
 
import java.util.ArrayList;
import java.util.List;
 
// 回文链表
//给你一个单链表的头节点 head ，请你判断该链表是否为回文链表。如果是，返回 true ；否则，返回 false 输入：head = [1,2,2,1]
//输出：true
public class Top22 {
    public static boolean isPalindrome(ListNode head) {
        List list = new ArrayList<>();
        while (head != null) {
            list.add(head.val);
            head = head.next;
        }
 
        int length = list.size();
 
        int k = length / 2;
        for (int i = 0; i <= k; i++) {
            if (list.get(i) != list.get(length - 1 - i)) {
                return false;
            }
        }
        return true;
    }
 
    public static void main(String[] args) {
        int[] nums = {1,2,3,2,1};
        ListNode node =  ListNode.setNodes(0,nums);
        ListNode.printListData(node);
 
        int[] nums2 = {1,0,0};
        System.out.println(isPalindrome(ListNode.setNodes(0,nums2)));
    }
}

ListNode 类

package Util;
 
public class ListNode {
    public int val;
    public ListNode next;
 
    public ListNode() {
    }
 
    public ListNode(int val) {
        this.val = val;
    }
 
    public ListNode(int val, ListNode next) {
        this.val = val;
        this.next = next;
    }
 
    public static ListNode setNodes(int index,int[] nums){
        ListNode res = new ListNode();
        res.val = nums[index];
        if(index == nums.length-1){
            res.next = null;
            return res;
        }
        else{
            res.next = setNodes(index+1,nums);
        }
        return res;
    }
 
    public static void printListData(ListNode node){
        while (node!=null){
            System.out.println(node.val);
            node = node.next;
        }
    }
}

harryptter / LeetcodeTop100 · GitCode