链表反转

反转链表需要3个本地变量

1. pre ：指向前一个节点
2. t ：当前节点
3. next：后一个节点

反转步骤

class Node {
    int value;
    Node next;
}

1、初始化变量

Node pre = null;
Node t = head;
Node next = null;

2、循环反转

while(t!=null){
    next = t.next;
    t.next = pre;
    pre = t;
    t = next;
}

完整代码

import java.util.StringJoiner;

public class ReverseLinkedList {
    public static void main(String[] args) {
        Node node = prepareNodeList();
        printNodeList(node);
        Node pre = null, t = node, next;
        while (t != null) {
            next = t.next;
            t.next = pre;
            pre = t;
            t = next;
        }
        printNodeList(pre);
    }

    static Node prepareNodeList() {
        int[] arr = new int[]{2, 4, 5, 6, 7, 8, 9};
        Node head = new Node(-1);
        Node t = head;
        for (int i : arr) {
            Node node = new Node(i);
            t.next = node;
            t = node;
        }
        return head.next;
    }

    static void printNodeList(Node node) {
        StringJoiner sj = new StringJoiner("-->");
        while (node != null) {
            sj.add(String.valueOf(node.x));
            node = node.next;
        }
        System.out.println(sj);
    }

    static class Node {
        int x;
        Node next;

        Node(int x) {
            this.x = x;
        }
    }
}