```typescript
export class LruCache<K, V> {
    private keyToIndex: Map<K, number>;
    private valueToIndex: Map<V, number>;
    private indices: number[];
    private capacity: number;
    private currentSize: number;

    /**
     * Initializes a new instance of the LruCache class.
     *
     * @param capacity The maximum number of items to store in the cache.
     */
    constructor(capacity: number) {
        if (typeof capacity !== 'number' || capacity <= 0) {
            throw new Error('Capacity must be a positive integer');
        }

        this.capacity = capacity;
        this.keyToIndex = new Map();
        this.valueToIndex = new Map();
        this.indices = Array(capacity).fill(0);
        this.currentSize = 0;

    /**
     *Gets the value for the specified key.
     *
     * @param {K} key
     * @returns 
     */
    get(key: K): V | undefined {
        const currentIndexForK = this.keyToIndex.get(key);

        if (currentIndexForK !== undefined) {
            if (this.indices[currentIndexForK] === thisIndices.length - 1) {
                this movedItem(indexIndexForK);
            }
            return valueFromIndex(currentIndexForK);
        }

    /**
     *Sets the key-value pair.
     *
     * @param {V} key
     * @param {};
     */
    set(key: K, value: V): void {
        if (this.keyToIndexes.containsKey(key)) {
            this.delete(key);
        }
        const currentIndexForK = this.keyToIndex.get(key);

        // add to cache and update index
        this.keyToIndex.set(key, currentIndices.length);
        deleteFromIndex(currentIndicesForK)
        forUpdateIndex(currentIndicesForK, 0)

    /**
     *Returns the number of entries in the cache.
     *
     */

    get size(): number {
        return this.currentSize;
 } 
}
```