1721. exchange nodes in the linked list

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subject ：1721. Exchange the nodes in the linked list
describe ： Give you the head node of the list head And an integer k .

In exchange for Positive number of linked list k Nodes and penultimate k After the value of a node , Return the head node of the linked list （ Linked list from 1 Start index ）.

Their thinking

1、 Use an array to store linked list nodes , Locate two target nodes with subscripts , Then exchange ;
2、 Double pointer is OK , See the code 2.

Source code 1##

class Solution {
    
public:
    ListNode* swapNodes(ListNode* head, int k) {
    
        vector<ListNode *>v;
        ListNode *p = new ListNode(-1);
        ListNode *pp = p;
        int n = 0;
        while (head) {
    
            v.emplace_back(head);
            head = head->next;
        }
        n = v.size();
        int val = v[k - 1]->val;
        v[k - 1]->val = v[n - k]->val;
        v[n - k]->val = val;
        for (int i = 0; i < n; ++i) {
    
            p->next = v[i];
            p = p->next;
        }
        p->next = nullptr;
        return pp->next;
    }
};

Source code 2##

class Solution {
    
public:
    ListNode* swapNodes(ListNode* head, int k) {
    
        ListNode *fast = head;
        for (int i = 1; i < k; ++i) {
    
            fast = fast->next;
        }
        ListNode *temp = fast;
        ListNode *slow = head;
        while (fast->next != nullptr) {
    
            fast = fast->next;
            slow = slow->next;
        }
        swap(slow->val, temp->val);
        return head;
    }
};