leetcode/cpp/0024.cpp at master · xfmeng17/leetcode · GitHub

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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:
  ListNode *swapPairs(ListNode *head) { return func1(head); }

  ListNode *func1(ListNode *head) {
    if (head == NULL || head->next == NULL) {
      return head;
    }

    ListNode *head0 = head;
    ListNode *curr0 = head0;
    ListNode *head1 = head->next;
    ListNode *curr1 = head1;
    ListNode *curr = head->next->next;
    int cnt = 2;
    while (curr != NULL) {
      if (cnt % 2 == 0) {
        curr0->next = curr;
        curr0 = curr;
      } else {
        curr1->next = curr;
        curr1 = curr;
      }
      curr = curr->next;
      cnt++;
    }
    curr0->next = NULL;
    curr1->next = NULL;

    head = head1;
    curr0 = head0;
    curr1 = head1;
    cnt = 1;
    while (curr0 != NULL && curr1 != NULL) {
      if (cnt % 2 == 0) {
        curr = curr0->next;
        curr0->next = curr1;
        curr0 = curr;
      } else {
        curr = curr1->next;
        curr1->next = curr0;
        curr1 = curr;
      }
      cnt++;
    }

    return head;
  }
};