206. 反转链表
解题思路
1.遍历转换为数组
2.数组反转，new ListNode
解题遇到的问题
1.头结点初始化和之后结点，变量赋值不同
后续需要总结学习的知识点
1.链表的遍历、插入、删除、添加，JDK源码阅读List的不同实现
##解法1
import java.util.ArrayList;
import java.util.List;
class Solution {
public static void main(String[] args) {
reverseList(new ListNode(1, new ListNode(2,
new ListNode(3, new ListNode(4, new ListNode(5))))));
}
/**
* 1.遍历转换为数组
* 2.数组反转，new ListNode
*/
public static ListNode reverseList(ListNode head) {
List<Integer> list = new ArrayList<Integer>();
while (head != null) {
list.add(head.val);
head = head.next;
}
ListNode result = null;
for (int i = list.size() - 1; i >= 0; i--) {
if (i == list.size() - 1) {
head = new ListNode(list.get(i));
result = head;
} else {
ListNode temp = new ListNode(list.get(i));
head.next = temp;
head = head.next;
}
}
return result;
}
public static class ListNode {
int val;
ListNode next;
ListNode() {
}
ListNode(int val) {
this.val = val;
}
ListNode(int val, ListNode next) {
this.val = val;
this.next = next;
}
}
}
