BM2 链表内指定区间反转(c++)_c++ 链表内指定区间反转

#include<iostream>
using namespace std;

struct ListNode{
    int val;
    struct ListNode* next;
    ListNode(int x):val(x),next(nullptr){};
};

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */


class Solution {
public:
    /**
     * 
     * @param head ListNode类 
     * @param m int整型 
     * @param n int整型 
     * @return ListNode类
     */
    ListNode* reverseBetween(ListNode* head, int m, int n) {
        // write code here
        ListNode* dummyNode = new ListNode(-1);
        dummyNode->next = head;
        
        ListNode*pre = dummyNode;
        // 第 1 步：从虚拟头节点走 left - 1 步，来到 left 节点的前一个节点
        // 建议写在 for 循环里，语义清晰
        for(int i = 0;i < m -1;i++){
            pre = pre->next;
        }
        
         // 第 2 步：从 pre 再走 right - left + 1 步，来到 right 节点
        ListNode* rightNode = pre;
        for(int i = 0; i < n -m + 1;i++){
            rightNode = rightNode->next;
        }
        // 第 3 步：切断出一个子链表（截取链表）
        ListNode* leftNode = pre->next;
        ListNode* cur = rightNode->next;
        
        // 注意：切断链接
        pre->next = nullptr;
        rightNode->next = nullptr;
        
        //第 4 步：同第 206 题，反转链表的子区间
        reverseList(leftNode);
        
        //第5步 接回原来的链表
        pre->next = rightNode;
        leftNode->next = cur;
        dummyNode = dummyNode->next;
        while(dummyNode){
            cout << dummyNode->val << " ";
            dummyNode = dummyNode->next;//打印反转后的值
        }
        return dummyNode;
        
    }
    
    void reverseList(ListNode* head){
        if(head == nullptr){
            return;
        }
        ListNode* pre = nullptr;
        while(head){
            ListNode*temp = head->next;
            head->next = pre;
            pre = head;
            head = temp;
        }
    }
};

int main(){
    int val;
    ListNode* head = new ListNode(0);
    ListNode* phead = head;
    while(cin >> val){
        ListNode* next_node = new ListNode(val);
        head = head->next = next_node;
    }
    phead = phead -> next;
//     while(phead){
//         cout << phead->val << " ";
//         phead = phead -> next;
//     }
    Solution s;
    s.reverseBetween(phead, 2, 4);
}

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