Q; input a linked list, output the k-th node from the bottom of the linked list.
A: Define two pointers:
(1) The first pointer traverses forward k-1 from the head pointer of the linked list, and the second pointer remains unchanged;
(2) Starting from the kth step, the second pointer also Start traversing from the head pointer of the linked list;
(3) Since the distance between the two pointers is kept at k-1, when the first (going in front) pointer reaches the end of the linked list, the second (going in the back) pointer is exactly the k-th penultimate a node.
/*
struct ListNode {
int val;
struct ListNode *next;
ListNode(int x) :
val(x), next(NULL) {
}
};*/
class Solution {
public:
ListNode* FindKthToTail(ListNode* pListHead, unsigned int k) {
ListNode* p1 = pListHead;
ListNode* p2 = pListHead;
if(NULL == pListHead || k <= 0)
{
return NULL;
}
for(int i = 0; i<k - 1; i++)
{
if(p1->next == NULL)
{
return NULL;
}
else
{
p1 = p1->next;
}
}
while(p1->next != NULL)
{
p1 = p1->next;
p2 = p2->next;
}
return p2;
}
};