import 'package:test/test.dart';

// Internal class to store each key-value pair and its next node

class Entry<K, V> {

final K key;

V value;

Entry<K, V> next;

Entry(this.key, this.value, [this.next]);

}

class HashMap<K, V> {

// Internal list to store the keys and values

List<Entry<K, V>> _table;

HashMap() {

_table = List<Entry<K, V>>.filled(256, null);

}

// Helper function to generate a hash code for a key

int _hashCode(K key) {

return key.hashCode % _table.length;

}

// Insert a new key-value pair into the hash map

void insert(K key, V value) {

final int index = _hashCode(key);

if (_table[index] == null) {

_table[index] = Entry<K, V>(key, value);

} else {

Entry<K, V> entry = _table[index];

while (entry.next != null && entry.key != key) {

entry = entry.next;

}

if (entry.key == key) {

entry.value = value;

} else {

entry.next = Entry<K, V>(key, value);

}

}

}

// Get the value associated with a key in the hash map

V get(K key) {

final int index = _hashCode(key);

if (_table[index] == null) {

return null;

} else {

Entry<K, V> entry = _table[index];

while (entry != null && entry.key != key) {

entry = entry.next;

}

return entry?.value;

}

}

}

void main() {

test('adding a key to a map', () {

HashMap map = HashMap();

expect(map.get(1), null);

map.insert(1, 'Akash');

expect(map.get(1), 'Akash');

});

test('updating a key in a map', () {

HashMap map = HashMap();

map.insert(1, 'Akash');

expect(map.get(1), 'Akash');

map.insert(1, 'IronMan');

expect(map.get(1), 'IronMan');

});

}