题目：输入一个链表，输出该链表中倒数第k 个结点．为了符合大多数人的习惯，本题从1 开始计数，即链表的尾结点是倒数第1 个结点．例如一个链表有6 个结点，从头结点开始它们的值依次是1 、2、3、4、5 、6。这个个链表的倒数第3 个结点是值为4 的结点。
代码如下：
package demo;
public class Test14 {
public static class ListNode {
int value;
ListNode next;
}
public static ListNode findKthToTail(ListNode head, int k) {
// 链表不能为null，k必须大于0
if(head == null || k < 1) {
return null;
}
ListNode behindPointer = head;
ListNode aheadPointer = head;
for(int i = 0; i < k-1; i++) {
if(aheadPointer.next != null) {
aheadPointer = aheadPointer.next;
} else {
return null;
}
}
while(aheadPointer.next != null) {
aheadPointer = aheadPointer.next;
behindPointer = behindPointer.next;
}
return behindPointer;
}
public static void main(String[] args) {
ListNode head = new ListNode();
head.value = 1;
head.next = new ListNode();
head.next.value = 2;
head.next.next = new ListNode();
head.next.next.value = 3;
head.next.next.next = new ListNode();
head.next.next.next.value = 4;
head.next.next.next.next = new ListNode();
head.next.next.next.next.value = 5;
head.next.next.next.next.next = new ListNode();
head.next.next.next.next.next.value = 6;
System.out.println("尾结点：");
System.out.println(findKthToTail(head, 1).value);
System.out.println("头结点：");
System.out.println(findKthToTail(head, 6).value);
System.out.println("第3个结点：");
System.out.println(findKthToTail(head, 3).value);
System.out.println("头结点为null：");
System.out.println(findKthToTail(null, 1));
System.out.println("链表结点个数小于k：");
System.out.println(findKthToTail(head, 10));
System.out.println("k为0：");
System.out.println(findKthToTail(head, 0));
}
}
运行结果
