字符串反转

C++实现字符串反转

最新推荐文章于 2025-11-27 15:16:14 发布

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#c++

#include <iostream>
#include <set>
#include <thread>
#include <mutex>
#include <deque>
using namespace std;


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) {}
};

// 翻转链表
ListNode* Reverse(ListNode* head) {
    ListNode pre(0, head);
    ListNode* cur = head;
    while(cur->next != nullptr) {
        auto tmp = cur->next;
        cur->next = tmp->next;
        tmp->next = pre.next;
        pre.next = tmp;
    }

    return pre.next;
}

// k个一组翻转链表，不足k个时不进行翻转，要求复用Reverse函数
// input:   head = {1, 2, 3, 4, 5}, k = 2
// output:  {2, 1, 4, 3, 5}
ListNode* reverseKGroup(ListNode* head, int k) {
    ListNode pre(0, head);
    ListNode* first = head;
    ListNode* second = head;
    ListNode* third = &pre;
    int num = k;
    while (first != nullptr) {
        num = k;
        while (num > 1 && first != nullptr) {
            first = first->next;
            num--;
        }

        if (first == nullptr) {
            third->next = second;
        } else {
             auto tmp_head = second;
            second = first->next;
            first->next = nullptr;
            third->next = Reverse(tmp_head);

            num = k;
            while (num > 0) {
                third = third->next;
                num--;
            }
            first = second;
        }
    }
    return pre.next;
}

int main() {
  ListNode* head = new ListNode(1);
  ListNode* cur = head;
  for (int i = 2; i <= 5; ++i) {
    cur->next = new ListNode(i);
    cur = cur->next;
  }
  ListNode* res = reverseKGroup(head, 2);
//   ListNode* res = Reverse(head);
  while (res) {
    std::cout << res->val << " ";
    res = res->next;
  }
  std::cout << std::endl;

  return 0;
}