<p>You are given the <code>head</code> of a linked list, and an integer <code>k</code>.</p>

<p>Return <em>the head of the linked list after <strong>swapping</strong> the values of the </em><code>k<sup>th</sup></code> <em>node from the beginning and the </em><code>k<sup>th</sup></code> <em>node from the end (the list is <strong>1-indexed</strong>).</em></p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/09/21/linked1.jpg" style="width: 400px; height: 112px;" />
<pre>
<strong>Input:</strong> head = [1,2,3,4,5], k = 2
<strong>Output:</strong> [1,4,3,2,5]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> head = [7,9,6,6,7,8,3,0,9,5], k = 5
<strong>Output:</strong> [7,9,6,6,8,7,3,0,9,5]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the list is <code>n</code>.</li>
	<li><code>1 &lt;= k &lt;= n &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= Node.val &lt;= 100</code></li>
</ul>

/**
 * 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 getIndex(ListNode*head ,ListNode*&frontIndex,ListNode*&backIndex,int& kFront,int&kback,int k,int&n){
        if(head == NULL ){
            return;

        }
        if(kFront == k){
            frontIndex = head;
        }
        n++;
        kback++;
        kFront++;

        getIndex(head->next,frontIndex,backIndex,kFront,kback,k,n);
        kback--;
        if(n-kback-1 == k){
            backIndex = head;
        }
    }
    ListNode* swapNodes(ListNode* head, int k) {
        
        ListNode*frontIndex = NULL;
        ListNode*backIndex = NULL;
        int kFront = 1;
        int kback = 0;
        int n=1;
        getIndex(head,frontIndex,backIndex,kFront,kback,k,n);
        if(frontIndex!=NULL){
            cout<<"fornt "<<frontIndex->val<<endl;
        }
        if(backIndex!=NULL){
            cout<<"bakc "<<backIndex->val<<endl;
        }
        if(backIndex!=NULL && frontIndex!=NULL){
            int a = backIndex->val;
            backIndex->val = frontIndex->val;
            frontIndex->val = a;
        }
        return head;
    }
};
193000