Reorder List

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:

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

Example 2:

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

Solution

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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:
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--];
}
}
};