fix #2251 (#2252)

DataStructures/DynamicArray/DynamicArray.java

@@ -11,6 +11,7 @@ import java.util.stream.StreamSupport;
  * @param <E> the type that each index of the array will hold
  */
 public class DynamicArray<E> implements Iterable<E> {
+	private static final int DEFAULT_CAPACITY = 16;
 
 	private int capacity;
 	private int size;
@@ -27,22 +28,11 @@ public class DynamicArray<E> implements Iterable<E> {
 		this.elements = new Object[this.capacity];
 	}
 
-  /** No-args constructor */
-  public DynamicArray() {
-    this.size = 0;
-    this.capacity = 10;
-    this.elements = new Object[this.capacity];
-  }
-
 	/**
-   * Doubles the capacity of the array
+	 * No-args constructor
-   *
-   * @return int the new capacity of the array
 	 */
-  public int newCapacity() {
+	public DynamicArray() {
-    this.capacity *= 2;
+		this(DEFAULT_CAPACITY);
-    // changed from this.capacity <<= 1; now much easier to understand
-    return this.capacity;
 	}
 
 	/**
@@ -52,7 +42,7 @@ public class DynamicArray<E> implements Iterable<E> {
 	 */
 	public void add(final E element) {
 		if (this.size == this.elements.length) {
-      this.elements = Arrays.copyOf(this.elements, newCapacity());
+			this.elements = Arrays.copyOf(this.elements, newCapacity(2 * this.capacity));
 		}
 
 		this.elements[this.size] = element;
@@ -89,6 +79,8 @@ public class DynamicArray<E> implements Iterable<E> {
 		final E oldElement = getElement(index);
 		fastRemove(this.elements, index);
 
+		if (this.capacity > DEFAULT_CAPACITY && size * 4 <= this.capacity)
+			this.elements = Arrays.copyOf(this.elements, newCapacity(this.capacity / 2));
 		return oldElement;
 	}
 
@@ -128,6 +120,11 @@ public class DynamicArray<E> implements Iterable<E> {
 		return (E) this.elements[index];
 	}
 
+	private int newCapacity(int capacity) {
+		this.capacity = capacity;
+		return this.capacity;
+	}
+
 	/**
 	 * returns a String representation of this object
 	 *