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leetcode 0143

admin 11月 13, 2020 0

Desicription

Given a singly linked list L: L0→L1→…→Ln-1→Ln,

reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…

You may not modify the values in the list’s nodes, only nodes itself may be changed.

Example 1:

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

Example 2:

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

Solution


 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class  {
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--];
        }
    }
};