LeetCode 0143 - Reorder List

Given 1->2->3->4, reorder it to 1->4->2->3.

Given 1->2->3->4->5, reorder it to 1->5->2->4->3.

/**
 * 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) {
        if(head == NULL)
            return ;
        vector<int> vec;
        for(auto it = head; it != NULL; it = it->next)
            vec.push_back(it->val);
        int left = 0;
        int right = vec.size()-1;
        for(auto it = head; it != NULL; it = it->next) {
            it->val = vec[left++];
            it = it->next;
            if(it == NULL)
                break;
            it->val = vec[right--];
        }
    }
};