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Partition_List.cc
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Partition_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:
ListNode *partition(ListNode *head, int x) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
ListNode *entry = NULL;
ListNode *pHead = NULL;
ListNode *pTail = NULL;
for (ListNode **pCnt = &head; *pCnt != NULL; ) {
entry = *pCnt;
if (entry->val < x) {
*pCnt = entry->next;
if (pHead == NULL) {
pHead = entry;
pTail = entry;
} else {
pTail->next = entry;
pTail = pTail->next;
}
} else {
pCnt = &(entry->next);
}
}
if (pTail != NULL) {
pTail->next = head;
return pHead;
}
return head;
}
};
//Another method using second level pointer
class Solution {
public:
ListNode *partition(ListNode *head, int x) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
ListNode *ret = NULL;
ListNode **tail = &ret;
ListNode **pHead = &head;
ListNode *entry = NULL;
for (ListNode **pCur = &head; *pCur; ) {
entry = *pCur;
if (entry->val < x) {
*pCur = entry->next;
*tail = entry;
tail = &(entry->next);
} else {
pCur = &(entry->next);
}
}
*tail = *pHead;
return ret;
}
};