[1721] Swapping Nodes in a Linked List

逋的廖喔～竟然一次PASS，只是要跑兩次迴圈XD

先把first version 貼上來～再來寫one pass 版

/**

* Definition for singly-linked list.

* struct ListNode {

* int val;

* struct ListNode *next;

* };

*/

struct ListNode* swapNodes(struct ListNode* head, int k){

if (head == NULL || head->next == NULL)

return head;

struct ListNode* ptr=head;

int count=0;

struct ListNode *fromhead, *fromend;

while (ptr!=NULL)

{

count++;

if (count==k)

fromhead = ptr;

ptr = ptr->next;

}

int target = count-k +1;

count = 0;

ptr=head;

while (ptr!=NULL)

{

count++;

if (count==target)

{

fromend = ptr;

break;

}

ptr = ptr->next;

}

int tmp = fromhead->val;

fromhead->val = fromend->val;

fromend->val = tmp;

return head;

}

啊啊啊～再次感受到自己的進步真的是很感動QQ 

但是漂亮的ONE PASS 解法我大概還是不會自己想到就是了 XD

struct ListNode* swapNodes(struct ListNode* head, int k){

if (head == NULL || head->next == NULL)

return head;

struct ListNode* ptr=head;

int count=0;

struct ListNode *fromhead, *fromend;

while (ptr!=NULL)

{

count++;

if (count==k)

{

fromhead = ptr;

fromend = head;

}

ptr = ptr->next;

if (count>k)

fromend = fromend->next;

}

int tmp = fromhead->val;

fromhead->val = fromend->val;

fromend->val = tmp;

return head;

}