done

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

@@ -1,19 +1,98 @@
 package core.basesyntax;
 
 public class MyHashMap<K, V> implements MyMap<K, V> {
+    private static final int DEFAULT_CAPACITY = 16;
+    private static final double LOAD_FACTOR = 0.75;
+    private static final int RESIZE_MULTIPLIER = 2;
+
+    private Node<K, V>[] table;
+    private int size;
+
+    public MyHashMap() {
+        table = (Node<K, V>[]) new Node[DEFAULT_CAPACITY];
+    }
 
     @Override
     public void put(K key, V value) {
+        if ((size + 1) > table.length * LOAD_FACTOR) {
+            resize();
+        }
+
+        int index = getIndex(key, table.length);
+        Node<K, V> current = table[index];
+
+        while (current != null) {
+            if (keysAreEqual(current.key, key)) {
+                current.value = value;
+                return;
+            }
+            current = current.next;
+        }
 
+        Node<K, V> newNode = new Node<>(key, value);
+        newNode.next = table[index];
+        table[index] = newNode;
+        size++;
     }
 
     @Override
     public V getValue(K key) {
+        int index = getIndex(key, table.length);
+        Node<K, V> current = table[index];
+
+        while (current != null) {
+            if (keysAreEqual(current.key, key)) {
+                return current.value;
+            }
+            current = current.next;
+        }
+
         return null;
     }
 
     @Override
     public int getSize() {
-        return 0;
+        return size;
+    }
+
+    private void resize() {
+        Node<K, V>[] oldTable = table;
+        table = (Node<K, V>[]) new Node[oldTable.length * RESIZE_MULTIPLIER];
+        size = 0;
+
+        for (Node<K, V> node : oldTable) {
+            while (node != null) {
+                put(node.key, node.value);
+                node = node.next;
+            }
+        }
+    }
+
+    private int getIndex(K key, int length) {
+        if (key == null) {
+            return 0;
+        }
+        return Math.abs(key.hashCode()) % length;
+    }
+
+    private boolean keysAreEqual(K firstKey, K secondKey) {
+        if (firstKey == null && secondKey == null) {
+            return true;
+        }
+        if (firstKey == null || secondKey == null) {
+            return false;
+        }
+        return firstKey.equals(secondKey);
+    }
+
+    private class Node<K, V> {
+        private V value;
+        private K key;
+        private Node<K, V> next;
+
+        private Node(K key, V value) {
+            this.key = key;
+            this.value = value;
+        }
     }
 }