单链表反转

public class ReverseListTest {
    static class Node {
        public int num;
        public Node next;

        public Node(int n) {
            this.num = n;
        }
    }

    public static void main(String[] args) {
        int[] src = new int[]{1, 2, 3, 4, 5};
        Node head = arrayToNode(src);
        printNode(head);
        Node newHead = reverseList(head);
        printNode(newHead);
    }

    public static Node arrayToNode(int[] arr) {
        Node head = new Node(arr[0]); // 把数组的第一个位置定义为头结点
        Node cur = head; // 一个指针，此时指向头结点
        for (int i = 1; i < arr.length; i++) { //头结点已经定义，从1开始
            //尾插法
            Node newNode = new Node(arr[i]);
            cur.next = newNode;
            cur = cur.next;
        }
        return head;
    }


    public static Node reverseList(Node head) {
        Node pre = null; //前指针节点
        Node cur = head; //当前指针节点
        Node next = null;
        while (cur != null) {
            next = cur.next; //临时保存当前节点的下一个节点
            cur.next = pre; //当前节点指向前面一个节点
            pre = cur; //前节点后移
            cur = next; //当前节点后移
        }
        return pre;
    }


    public static void printNode(Node node) {
        while (node != null) {
            System.out.print(node.num + " ");
            node = node.next;
        }
        System.out.println();
    }
}

输出：

image.png