leetcode-algorithms-143 Reorder List

leetcode-algorithms-143 Reorder List

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:

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

Example 2:

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

解法

/**
 * 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 == nullptr)
            return;
        
        std::vector<ListNode *> v;
        ListNode *p = head;
        while(p != nullptr) {
            v.push_back(p);
            p = p->next;
        }
        
        int left = 0;
        int right = v.size() - 1;
        bool odd = true;
        while(left < right) {
            if (odd)
                v[left++]->next = v[right];
            else
                v[right--]->next = v[left];
            odd = !odd;
        }
        v[left]->next = nullptr;
        
    }
};