1 files changed, 238 insertions, 0 deletions
diff --git a/src/main/java/bjc/esodata/MinMaxList.java b/src/main/java/bjc/esodata/MinMaxList.java
new file mode 100644
index 0000000..6747831
--- /dev/null
+++ b/src/main/java/bjc/esodata/MinMaxList.java
@@ -0,0 +1,238 @@
+package bjc.esodata;
+
+import java.util.*;
+
+// @FIXME Nov 15th, 2020 Ben Culkin :RecalcMinMax
+// Is there some sort of way to avoid having to recalculate these elements when
+// that element is removed?
+/**
+ * A list that automatically tracks the minimum & maximum element of a list.
+ * 
+ * @author Ben Culkin
+ * 
+ * @param <ValueType> The type of element stored in the list.
+ *
+ */
+public class MinMaxList<ValueType> extends AbstractList<ValueType> {
+	private final List<ValueType>       backing;
+	private final Comparator<ValueType> picker;
+	
+	private ValueType minElement;
+	private boolean recalcMin = false;
+	
+	private ValueType maxElement;
+	private boolean recalcMax = false;
+	
+	// Create constructors
+	
+	/**
+	 * Create a new min/max list using the given comparator.
+	 * 
+	 * @param picker The comparator to use to determine min/max elements.
+	 */
+	public MinMaxList(Comparator<ValueType> picker) {
+		this(picker, new ArrayList<>());
+	}
+	
+	/**
+	 * Create a new min/max list using the given comparator.
+	 * 
+	 * @param picker The comparator to use to determine min/max elements.
+	 * @param values The values to fill the list from.
+	 */
+	@SafeVarargs
+	public MinMaxList(Comparator<ValueType> picker, ValueType... values) {
+		this(picker);
+		
+		for (ValueType value : values) {
+			add(value);
+		}
+	}
+	/**
+	 * Create a new min/max list using the given comparator.
+	 * 
+	 * @param picker The comparator to use to determine min/max elements.
+	 * @param backing The collection to use values from.
+	 */
+	public MinMaxList(Comparator<ValueType> picker, Collection<ValueType> backing) {
+		this(picker, new ArrayList<>(backing));
+	}
+	
+	/**
+	 * Create a new min/max list using the given comparator.
+	 * 
+	 * @param picker The comparator to use to determine min/max elements.
+	 * @param backing The list to use as a backing list.
+	 */
+	public MinMaxList(Comparator<ValueType> picker, List<ValueType> backing) {
+		this.backing = backing;
+		this.picker  = picker;
+		
+		calculateBoth();
+	}
+	
+	@Override
+	public ValueType get(int index) {
+		return backing.get(index);
+	}
+
+	@Override
+	public ValueType set(int index, ValueType element) {
+		ValueType oldElement = backing.set(index, element);
+	
+		if (minElement == null) {
+			minElement = element;
+		} else if (picker.compare(element, minElement) < 0) {
+			minElement = element;
+			recalcMin = false;
+		} else if (oldElement.equals(minElement)) {
+			minElement = null;
+			recalcMin = true;
+		}
+		
+		if (maxElement == null) {
+			maxElement = element;
+		} else if (picker.compare(element, maxElement) > 0) {
+			maxElement = element;
+			recalcMax = false;
+		} else if (oldElement.equals(maxElement)) {
+			maxElement = null;
+			recalcMax = true;
+		}
+		
+		return oldElement;
+	}
+	
+	@Override
+	public void add(int index, ValueType element) {
+		backing.add(index, element);
+		
+		if (minElement == null) {
+			minElement = element;
+		} else if (picker.compare(element, minElement) < 0) {
+			minElement = element;
+			recalcMin = false;
+		}
+		
+		if (maxElement == null) {
+			maxElement = element;
+		} else if (picker.compare(element, maxElement) > 0) {
+			maxElement = element;
+			recalcMax = false;
+		} 
+	}
+	
+	@Override
+	public ValueType remove(int index) {
+		ValueType oldElement = backing.remove(index);
+		
+		if (oldElement.equals(minElement)) {
+			minElement = null;
+			recalcMin = true;
+		}
+		
+		if (oldElement.equals(maxElement)) {
+			maxElement = null;
+			recalcMax = true;
+		}
+		
+		return oldElement;
+	}
+	
+	@Override
+	public int size() {
+		return backing.size();
+	}
+
+	/**
+	 * Get the minimum element currently stored in this list.
+	 * 
+	 * @return The minimum element stored in the list.
+	 */
+	public ValueType minimum() {
+		if (recalcMin) calculateMinimum();
+		
+		return minElement;
+	}
+
+	/**
+	 * Get the maximum element currently stored in this list.
+	 * 
+	 * @return The maximum element stored in the list.
+	 */
+	public ValueType maximum() {
+		if (recalcMax) calculateMaximum();
+		
+		return maxElement;
+	}
+	
+	private void calculateMinimum() {
+		for (ValueType element : backing) {
+			if (minElement == null) {
+				minElement = element;
+			} else if (picker.compare(element, minElement) < 0) {
+				minElement = element;
+			}			
+		}
+		
+		recalcMin  = false;
+	}
+	
+	private void calculateMaximum() {
+		for (ValueType element : backing) {
+			if (maxElement == null) {
+				maxElement = element;
+			} else if (picker.compare(element, maxElement) > 0) {
+				maxElement = element;
+			}
+		}
+
+		recalcMax  = false;
+	}
+	
+	private void calculateBoth() {
+		for (ValueType element : backing) {
+			if (minElement == null) {
+				minElement = element;
+			} else if (picker.compare(element, minElement) < 0) {
+				minElement = element;
+			}		
+			
+			if (maxElement == null) {
+				maxElement = element;
+			} else if (picker.compare(element, maxElement) > 0) {
+				maxElement = element;
+			}
+		}
+
+		recalcMin  = false;
+		recalcMax  = false;
+	}
+
+	@Override
+	public String toString() {
+		return String.format("%s (min: %s) (max: %s)", backing,
+				recalcMin ? "(unknown)" : minElement,
+				recalcMax ? "(unknown)" : maxElement);
+	}
+	
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = super.hashCode();
+		result = prime * result + Objects.hash(backing, picker);
+		return result;
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj)                  return true;
+		if (!super.equals(obj))           return false;
+		if (getClass() != obj.getClass()) return false;
+		
+		MinMaxList<?> other = (MinMaxList<?>) obj;
+	
+		return Objects.equals(backing, other.backing)
+				&& Objects.equals(picker, other.picker);
+	}
+}