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Recorder_List.cc
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Recorder_List.cc
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/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
void reorderList(ListNode *head) {
// IMPORTANT: Please reset any member data you declared, as
// the same Solution instance will be reused for each test case.
head = mergeList(head, reverseList(splitList(head)));
return;
}
private:
ListNode *splitList(ListNode * head) {
if (!head)
return NULL;
ListNode *fast = head, *slow = head;
while (fast && fast->next) {
fast = fast->next->next;
slow = slow->next;
}
fast = slow->next;
slow->next = NULL;
return fast;
}
ListNode *reverseList(ListNode *head) {
ListNode *pre = NULL, *cur = head, *nxt = NULL;
while (cur) {
nxt = cur->next;
cur->next = pre;
pre = cur;
cur = nxt;
}
return pre;
}
ListNode *mergeList(ListNode *ha, ListNode *hb) {
ListNode *ret = NULL;
ListNode **pCur = &ret;
while (ha && hb) {
*pCur = ha;
pCur = &(ha->next);
ha = ha->next;
*pCur = hb;
pCur = &(hb->next);
hb = hb->next;
}
*pCur = ha;
return ret;
}
};