(2.2) Return Kth to Last

Implement an algorithm to find the \(k\)th to last element of a singly-linked list.

For this solution, I’ll be using the LinkedList class that I created back in Problem 2.1.

function findKthValueUsingBuffer<T>(input: LinkedList<T>, k: number) {
    let current = input.head;
    let buffer = new Array(0);

    while(current != null) {
        if (buffer.length == k) {
            buffer.shift();
        }
        buffer.push(current.data);
        current = current.next;
    }
    return buffer.length == k ? buffer[0] : null;
}

function findKthValueDoubleIterate<T>(input: LinkedList<T>, k: number) {
    let current = input.head;
    let length = 0;

    while(current != null) {
        length++;
        current = current.next;
    }

    if (k < length) {
        current = input.head;
        for (let i = 0; i < length - k; i++) {
            current = current?.next || null;
        }
    }
    return k < length ? current?.data || null : null;
}