328. Odd Even Linked List

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problem

solution

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class Solution {
public:
    ListNode* oddEvenList(ListNode* head) {
        if(!head ||!head->next) return head;
        ListNode *odd= new ListNode (-1), *a = odd, *even = new ListNode(-1), *b = even;
        ListNode * p = head;
        while(p ){
            odd->next = p;
            odd=odd->next;
            p=p->next;
            if(p){
                even->next = p;
                p=p->next;
                even = even->next;
            }    
        }
        even->next = nullptr;
        odd->next = b->next;
        return a->next;
    }
};

analysis

  • time complexity O(n)
  • space complexity O(1)