Swap Kth Node Values - Amazon Top Interview Questions

Problem Statement :

You are given a singly linked list node and an integer k. Swap the value of the k-th (0-indexed) node from the end with the k-th node from the beginning.


1 ≤ n ≤ 100,000 where n is the number of nodes in node
0 ≤ k < n

Example 1


node = [1, 2, 3, 4, 5, 6]
k = 1


[1, 5, 3, 4, 2, 6]


We swap 2 and 5.

Example 2


node = [0, 6, 8, 2, 9]
k = 2


[0, 6, 8, 2, 9]


We swap 8 with 8.

Solution :


                        Solution in C++ :

LLNode* solve(LLNode* node, int k) {
    LLNode* dummy = new LLNode(-1, node);
    auto begin = node, end = node, temp = node, prevbegin = dummy, prevend = dummy;
    while (k--) {
        prevbegin = begin;
        begin = begin->next;
        temp = temp->next;
    while (temp->next) {
        prevend = end;
        temp = temp->next;
        end = end->next;
    prevbegin->next = end;
    prevend->next = begin;
    auto bnex = begin->next;
    begin->next = end->next;
    end->next = bnex;
    return dummy->next;

                        Solution in Python : 
class Solution:
    def solve(self, node, k):
        prev = node
        curr = node
        first = node

        while curr.next != None:
            curr = curr.next
            if k > 0:
                first = first.next

            if k <= 0:
                prev = prev.next
            k -= 1

        first.val, prev.val = prev.val, first.val
        return node

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