【算法】链表翻转的两种写法

初始化

ListNode listNode5 = new ListNode(5, null);
ListNode listNode4 = new ListNode(4, listNode5);
ListNode listNode3 = new ListNode(3, listNode4);
ListNode listNode2 = new ListNode(2, listNode3);
ListNode listNode1 = new ListNode(1, listNode2);
doReverse(listNode1);

遍历

private static ListNode doReverse(ListNode head) {
    ListNode prev = null, next;
    while (head != null) {
        next = head.next;
        head.next = prev;
        prev = head;
        head = next;
    }
    return prev;
}

递归

private static ListNode doReverse(ListNode head) {
    if (head == null || head.next == null) {
        return head;
    }
    ListNode newHead = doReverse(head.next);
    head.next.next = head;
    head.next = null;
    return newHead;
}