Leetcode 1721

The idea of this solution is pretty simple.

First, we find the length of the linked list
Next, we iterate through the linked list up until the ending kth node
And then we iterate through the linked list to to kth node
Then, last of all, switch the value of the kth node with the value of the kth node from the end.

Finding the length of the linked list is pretty simple. Just get a counter. In this problem, it is lengthOfLinkedList, then iterate through the linked list and add one to the counter every iteration.

We get the kth node from the end by iterating a counter i through 0 to lengthOfLinkedList - k, lengthOfLinkedList - k gets the length of the linked list and then subtracts k from it, so we get the ending kth node.

We get the kth node by just iterating through 0 to k - 1. We do k - 1 because we do first = first.Next which makes it the next value.

Then we switch the two values by just assigning them to each other if you don’t understand second.Val, first.Val = first.Val, second.Val it is basically:

temp := second.Val

second.Val = first.Val
first.Val = temp

The code:

func swapNodes(head *ListNode, k int) *ListNode {
    first := head
    second := head
    findLength := head
    lengthOfLinkedList := 0

    for findLength != nil {
        lengthOfLinkedList++
        findLength = findLength.Next
    }

    for i := 0; i < lengthOfLinkedList-k; i++ {
        second = second.Next
    }

    for i := 0; i < k-1; i++ {
        first = first.Next
    }

    second.Val, first.Val = first.Val, second.Val
    return head
}