leetcode hot 03

合集 - leetcode hot100(25)

1.leetcode hot 0102-152.leetcode hot 0202-153.leetcode hot 0402-16

4.leetcode hot 0302-15

5.leetcode hot 0502-176.leetcode hot 0602-197.leetcode hot 0702-208.leetcode hot 0802-219.leetcode hot 0902-2110.leetcode hot 1002-2411.leetcode hot 1202-2512.leetcode hot 1302-2613.leetcode hot 1402-2814.leetcode hot 1503-0115.leetcode hot 1103-0316.leetcode hot 1603-0317.leetcode hot 1703-0318.leetcode hot 1803-0319.leetcode hot 1903-0420.leetcode hot 2003-0521.leetcode hot 2103-0522.leetcode hot 2203-1223.leetcode hot 2303-1224.leetcode hot 2403-1225.leetcode hot 2503-12

收起

解题思路：找个容器将这个链表遍历一遍存下来，然后再对比；或者用数组列表存下来，双指针前后对比

/**
 * Definition for singly-linked list.
 * public 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 boolean isPalindrome(ListNode head) {
        if(head == null){
            return false;
        }
        ListNode dummy_head = new ListNode();
        ListNode p = head;
        while(p!=null){
            ListNode q = new ListNode(p.val,dummy_head.next);
            dummy_head.next = q;
            p = p.next;
        }
        ListNode head1 = dummy_head.next;
        while(head1!=null){
            if(head1.val!=head.val) return false;
            head1 = head1.next;
            head = head.next;
        }
        return true;

    }
}

/**
 * Definition for singly-linked list.
 * public 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 boolean isPalindrome(ListNode head) {
        //  数组加双指针
        List<Integer> list = new ArrayList<>();
        while(head!=null){
            list.add(head.val);
            head = head.next;
        }
        int left = 0;
        int right = list.size()-1;
        while(left<right){
            if(list.get(left) != list.get(right)) return false;
            left++;
            right--;
        }
        return true;
    }
}