Leetcode 92. 反转链表 II

代码

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:

    void reverseList(ListNode* head) {
        ListNode* pre = nullptr;
        ListNode* cur = head;
        while (cur) {
            ListNode* next = cur->next;
            cur->next = pre;
            pre = cur;
            cur = next;
        }
    }
    
    ListNode* reverseBetween(ListNode* head, int m, int n) {
        // write code here
        ListNode* dumyNode = new ListNode(0);
        dumyNode->next = head;
        
        // find pre left right succ node
        ListNode* pre = dumyNode;
        for (int i = 0; i < m - 1; i++)
            pre = pre->next;
        ListNode* left = pre->next;
        ListNode* right = pre;
        for (int i = 0; i < n - m + 1; i++)
            right = right->next;
        ListNode* succ = right->next;
        
        // 切断连接
        pre->next = nullptr;
        right->next = nullptr;
        
        reverseList(left);
        pre->next = right;
        left->next = succ;
        return dumyNode->next;

    }
};