fix: support null keys with occupied slots

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

@@ -6,12 +6,14 @@ public class MyHashMap<Key, Value> {
 
   private Key[] keys;
   private Value[] values;
+  private boolean[] occupied;
   private boolean[] deleted;
   private int size;
 
   public MyHashMap(int capacity) {
     keys = createArray(capacity);
     values = createArray(capacity);
+    occupied = new boolean[capacity];
     deleted = new boolean[capacity];
   }
 
@@ -26,26 +28,19 @@ public class MyHashMap<Key, Value> {
       resize();
     }
 
-    int index = index(key);
-    int start = index;
+    int index = findIndex(key);
 
-    while (keys[index] != null || deleted[index]) {
-      if (!deleted[index] && Objects.equals(keys[index], key)) {
-        Value oldValue = values[index];
-        values[index] = value;
-        return oldValue;
-      }
-
-      index = (index + 1) % keys.length;
-
-      if (index == start) {
-        resize();
-        return put(key, value);
-      }
+    if (index != -1) {
+      Value oldValue = values[index];
+      values[index] = value;
+      return oldValue;
     }
 
+    index = findEmptyIndex(key);
+
     keys[index] = key;
     values[index] = value;
+    occupied[index] = true;
     deleted[index] = false;
     size++;
 
@@ -60,6 +55,7 @@ public class MyHashMap<Key, Value> {
     }
 
     Value oldValue = values[index];
+    occupied[index] = false;
     deleted[index] = true;
     size--;
 
@@ -70,8 +66,8 @@ public class MyHashMap<Key, Value> {
     int index = index(key);
     int start = index;
 
-    while (keys[index] != null || deleted[index]) {
-      if (!deleted[index] && Objects.equals(keys[index], key)) {
+    while (occupied[index] || deleted[index]) {
+      if (occupied[index] && Objects.equals(keys[index], key)) {
         return index;
       }
 
@@ -85,22 +81,43 @@ public class MyHashMap<Key, Value> {
     return -1;
   }
 
+  private int findEmptyIndex(Key key) {
+    int index = index(key);
+    int start = index;
+    int deletedIndex = -1;
+
+    while (occupied[index]) {
+      if (Objects.equals(keys[index], key)) {
+        return index;
+      }
+
+      index = (index + 1) % keys.length;
+
+      if (index == start) {
+        return deletedIndex;
+      }
+    }
+
+    return deletedIndex == -1 ? index : deletedIndex;
+  }
+
   private int index(Key key) {
-    return Math.floorMod(key.hashCode(), keys.length);
+    return Math.floorMod(key == null ? 0 : key.hashCode(), keys.length);
   }
 
   private void resize() {
     Key[] oldKeys = keys;
     Value[] oldValues = values;
-    boolean[] oldDeleted = deleted;
+    boolean[] oldOccupied = occupied;
 
     keys = createArray(oldKeys.length * 2);
     values = createArray(oldValues.length * 2);
+    occupied = new boolean[keys.length];
     deleted = new boolean[keys.length];
     size = 0;
 
     for (int i = 0; i < oldKeys.length; i++) {
-      if (oldKeys[i] != null && !oldDeleted[i]) {
+      if (oldOccupied[i]) {
         put(oldKeys[i], oldValues[i]);
       }
     }