first solution

src/main/java/core/basesyntax/MyHashMap.java

@@ -1,19 +1,92 @@
 package core.basesyntax;
 
+import java.util.Objects;
+
 public class MyHashMap<K, V> implements MyMap<K, V> {
+    private static final int DEFAULT_INITIAL_CAPACITY = 16;
+    private static final float DEFAULT_LOAD_FACTOR = 0.75f;
+    private static final int HASH_MASK = Integer.MAX_VALUE;
+
+    public MyHashMap() {
+        table = new Node[DEFAULT_INITIAL_CAPACITY];
+        threshold = (int) (DEFAULT_INITIAL_CAPACITY * DEFAULT_LOAD_FACTOR);
+    }
 
     @Override
     public void put(K key, V value) {
+        if (size >= threshold) {
+            resize();
+        }
+        int hash = hash(key);
+        int index = (hash & HASH_MASK) % table.length;
+        Node<K, V> current = table[index];
+        while (current != null) {
+            if (current.hash == hash && Objects.equals(current.key, key)) {
+                current.value = value;
+                return;
+            }
+            current = current.next;
+        }
 
+        Node<K, V> newNode = new Node<>(hash, key, value, table[index]);
+        table[index] = newNode;
+        size++;
     }
 
     @Override
     public V getValue(K key) {
+        int hash = hash(key);
+        int index = (hash & HASH_MASK) % table.length;
+        Node<K, V> current = table[index];
+        while (current != null) {
+            if (current.hash == hash && Objects.equals(current.key, key)) {
+                return current.value;
+            }
+            current = current.next;
+        }
         return null;
     }
 
     @Override
     public int getSize() {
-        return 0;
+        return size;
     }
+
+    private void resize() {
+        int newCapacity = table.length * 2;
+        Node<K, V>[] newTable = new Node[newCapacity];
+        for (Node<K, V> node : table) {
+            while (node != null) {
+                Node<K, V> next = node.next;
+                int index = (node.hash & HASH_MASK) % newCapacity;
+                node.next = newTable[index];
+                newTable[index] = node;
+                node = next;
+            }
+        }
+        table = newTable;
+        threshold = (int) (newCapacity * DEFAULT_LOAD_FACTOR);
+    }
+
+    private int hash(K key) {
+        return key == null ? 0 : key.hashCode();
+    }
+
+    private class Node<K, V> {
+        private final int hash;
+        private final K key;
+        private V value;
+        private Node<K, V> next;
+
+        public Node(int hash, K key, V value, Node<K, V> next) {
+            this.hash = hash;
+            this.key = key;
+            this.value = value;
+            this.next = next;
+        }
+    }
+
+    private Node<K, V>[] table;
+    private int size;
+    private int threshold;
 }