done

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

@@ -1,19 +1,148 @@
 package core.basesyntax;
 
 public class MyHashMap<K, V> implements MyMap<K, V> {
+    private static final int initialCapacity = 16;
+    private static final int sizeMultiplier = 2;
+    private static final double loadFactor = 0.75;
+    private int currentMaxSize = initialCapacity;
+    private int threshold = (int) (initialCapacity * loadFactor);
+    private Node<K, V>[] buckets;
+    private int size = 0;
+
+    public MyHashMap() {
+        buckets = new Node[initialCapacity];
+    }
 
     @Override
     public void put(K key, V value) {
+        if (size >= threshold) {
+            resize();
+        }
+
+        int index = getIndexByKey(key);
+
+        if (buckets[index] == null) {
+            buckets[index] = new Node<>(key, value);
+            size++;
+            return;
+        }
+
+        Node<K, V> current = buckets[index];
+
+        if (current.key == null
+                ? key == null
+                : current.key.equals(key)) {
+            current.value = value;
+            return;
+        }
+
+        while (current.next != null) {
+            if (current.next.key == null
+                    ? key == null
+                    : current.next.key.equals(key)) {
+                current.next.value = value;
+                return;
+            }
+            current = current.next;
+        }
 
+        current.next = new Node<>(key, value);
+        size++;
     }
 
     @Override
     public V getValue(K key) {
+        if (size == 0) {
+            return null;
+        }
+
+        int index = getIndexByKey(key);
+        Node<K, V> current = buckets[index];
+
+        while (current != null) {
+            if (current.key == null
+                    ? key == null
+                    : current.key.equals(key)) {
+                return current.value;
+            }
+            current = current.next;
+        }
+
         return null;
     }
 
     @Override
     public int getSize() {
-        return 0;
+        return size;
+    }
+
+    private void addNewNode(Node<K, V> newNode) {
+        newNode.next = null;
+
+        int index = getIndexByKey(newNode.key);
+
+        if (buckets[index] == null) {
+            buckets[index] = newNode;
+            return;
+        }
+
+        Node<K, V> current = buckets[index];
+
+        if (current.key == null
+                ? newNode.key == null
+                : current.key.equals(newNode.key)) {
+            current.value = newNode.value;
+            return;
+        }
+
+        while (current.next != null) {
+            if (current.next.key == null
+                    ? newNode.key == null
+                    : current.next.key.equals(newNode.key)) {
+                current.next.value = newNode.value;
+                return;
+            }
+            current = current.next;
+        }
+
+        current.next = newNode;
+    }
+
+    private void resize() {
+        currentMaxSize = currentMaxSize * sizeMultiplier;
+        threshold = (int) (currentMaxSize * loadFactor);
+
+        Node<K, V>[] oldBuckets = buckets;
+        buckets = new Node[currentMaxSize];
+
+        for (Node<K, V> node : oldBuckets) {
+            while (node != null) {
+                Node<K, V> next = node.next;
+                node.next = null;
+                addNewNode(node);
+                node = next;
+            }
+        }
+    }
+
+    private int getIndexByKey(K key) {
+        if (key == null) {
+            return 0;
+        }
+
+        int hash = key.hashCode();
+        int hashMask = 0x7fffffff;
+        return (hash & hashMask) % currentMaxSize;
+    }
+
+    private static class Node<K, V> {
+        private final K key;
+        private V value;
+        private Node<K, V> next;
+
+        Node(K key, V value) {
+            this.key = key;
+            this.value = value;
+        }
     }
 }