feat: implement custom MyHashMap

second-part/hw-01/src/app/src/main/java/org/example/MyHashMap.java

@@ -0,0 +1,120 @@
+package org.example;
+
+public class MyHashMap<Key, Value> {
+
+  private Key[] keys;
+  private Value[] values;
+  private boolean[] deleted;
+  private int size;
+
+  public MyHashMap(int capacity) {
+    keys = createArray(capacity);
+    values = createArray(capacity);
+    deleted = new boolean[capacity];
+  }
+
+  public Value get(Key key) {
+    int index = findIndex(key);
+
+    return index == -1 ? null : values[index];
+  }
+
+  public Value put(Key key, Value value) {
+    if (size == keys.length) {
+      resize();
+    }
+
+    int index = findEmptyIndex(key);
+    if (keys[index] != null) {
+      Value oldValue = values[index];
+      values[index] = value;
+      return oldValue;
+    }
+
+    keys[index] = key;
+    values[index] = value;
+    deleted[index] = false;
+    size++;
+
+    return null;
+  }
+
+  public Value remove(Key key) {
+    int index = findIndex(key);
+
+    if (index == -1) {
+      return null;
+    }
+
+    Value oldValue = values[index];
+    deleted[index] = true;
+    size--;
+
+    return oldValue;
+  }
+
+  private int findIndex(Key key) {
+    int index = index(key);
+    int start = index;
+
+    while (keys[index] != null || deleted[index]) {
+      if (!deleted[index] && java.util.Objects.equals(keys[index], key)) {
+        return index;
+      }
+
+      index = (index + 1) % keys.length;
+
+      if (index == start) {
+        return -1;
+      }
+    }
+
+    return -1;
+  }
+
+  private int findEmptyIndex(Key key) {
+    int index = index(key);
+    int start = index;
+
+    while (keys[index] != null && !deleted[index]) {
+      if (java.util.Objects.equals(keys[index], key)) {
+        return index;
+      }
+
+      index = (index + 1) % keys.length;
+
+      if (index == start) {
+        resize();
+        return findEmptyIndex(key);
+      }
+    }
+
+    return index;
+  }
+
+  private int index(Key key) {
+    return Math.floorMod(key == null ? 0 : key.hashCode(), keys.length);
+  }
+
+  private void resize() {
+    Key[] oldKeys = keys;
+    Value[] oldValues = values;
+    boolean[] oldDeleted = deleted;
+
+    keys = createArray(oldKeys.length * 2);
+    values = createArray(oldValues.length * 2);
+    deleted = new boolean[keys.length];
+    size = 0;
+
+    for (int i = 0; i < oldKeys.length; i++) {
+      if (oldKeys[i] != null && !oldDeleted[i]) {
+        put(oldKeys[i], oldValues[i]);
+      }
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  private <T> T[] createArray(int capacity) {
+    return (T[]) new Object[capacity];
+  }
+}