[2816] Double a Number Represented as a Linked List

什麼？？？ 原來不是叫我全部展開乘以二再存回去嗎XD

可惡XD！

好吧至少我順便複習了一下reverse linked list. 

超過數字範圍的版本兒～～～～～

/**

* Definition for singly-linked list.

* struct ListNode {

* int val;

* struct ListNode *next;

* };

*/

struct ListNode* reverse(struct ListNode* head) {

struct ListNode *pre,*curr,*next;

pre = NULL;

curr = head;

next = curr->next;

while(next != NULL)

{

curr->next = pre;

pre = curr;

curr = next;

next = next->next;

}

curr->next = pre;

return curr;

}

struct ListNode* doubleIt(struct ListNode* head) {

unsigned long long num=0;

struct ListNode* ptr = head;

while (ptr != NULL)

{

num = num*10 + ptr->val;

ptr=ptr->next;

}

unsigned long long dou_num = num*2;

ptr =head;

while (dou_num>=10)

{

int tmp = dou_num%10;

dou_num /= 10;

if (ptr->next == NULL)

{

ptr->next = calloc (1, sizeof(struct ListNode));

}

ptr ->val = tmp;

ptr = ptr->next;

}

ptr->val = dou_num;

return reverse(head);

}

改成反轉之後一路相乘～再反轉回來～簡直歡樂 XD

是說久沒有reverse , 多了一行！可以再精進一下QQ

/**

* Definition for singly-linked list.

* struct ListNode {

* int val;

* struct ListNode *next;

* };

*/

struct ListNode* reverse(struct ListNode* head) {

struct ListNode *pre,*curr,*next;

pre = NULL;

curr = head;

next = curr->next;

while(next != NULL)

{

curr->next = pre;

pre = curr;

curr = next;

next = next->next;

}

curr->next = pre;

return curr;

}

struct ListNode* doubleIt(struct ListNode* head) {

struct ListNode* ptr = reverse(head);

head = ptr;

int carry = 0;

while (ptr != NULL)

{

int num = 2* (ptr->val)+ carry;

carry = (num>=10)?(num/10):(0);

ptr->val = num%10;

if (ptr->next == NULL && carry>0)

ptr->next = calloc (1, sizeof(struct ListNode));

ptr=ptr->next;

}

return reverse(head);

}