[leetcodeブラシ問題まとめ]Reverse Linked List II

くどくど書いてるみたいだけど、そうしましょう.将来2回目の計画を立てたら、もっと簡略化します.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *reverseBetween(ListNode *head, int m, int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(head == 0)
            return 0;
        if(n == m)
            return head;
        ListNode * last_head = 0;
        ListNode * first = 0;
        ListNode * pre = 0;
        ListNode * now = head;
        int cur = 1;
        while(now){
            ListNode * next = now->next;
            if(cur == m){
                last_head = pre;
                first = now;
                pre = now;
                now = next;
            }else if(cur == n){
                now->next = pre;
                first->next = next;
                if(m == 1)
                    return now;
                else{
                    last_head->next = now;
                    return head;
                }
            }
            else if(cur > m){
                now->next = pre;
                pre = now;
                now = next;
            }
            else{
                pre = now;
                now = next;
            }
            ++cur;
        }
    }
};