题解 | 反转链表

/**
 * class ListNode(var `val`: Int) {
 *     var next: ListNode? = null
 * }
 */
object Solution {
    /**
    * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
    *
    * 
        * @param head ListNode类 
        * @return ListNode类
    */
    fun ReverseList(head: ListNode?): ListNode?  {
        var cur = head
        var pre:ListNode ?= null
        var next :ListNode ?= null
        while (cur!=null){
            next = cur.next
            cur.next = pre
            pre = cur
            cur = next
        }
        return pre
    }
}