// Copyright (c) 2003-2012, Jodd Team (jodd.org). All Rights Reserved.
package jodd.util;
import java.util.Comparator;
import java.util.List;
/**
* Binary search wrapper over any type of user-defined collection.
* It provides a finder for given element, but also finder of first
* and last index in range of equal elements.
*/
public abstract class BinarySearch<E> {
/**
* Creates binary search wrapper over a list of comparable elements.
*/
public static <T extends Comparable> BinarySearch<T> forList(final List<T> list) {
return new BinarySearch<T>() {
@Override
@SuppressWarnings( {"unchecked"})
protected int compare(int index, T element) {
return list.get(index).compareTo(element);
}
@Override
protected int getLastIndex() {
return list.size() - 1;
}
};
}
/**
* Creates binary search wrapper over a list with given comparator.
*/
public static <T> BinarySearch<T> forList(final List<T> list, final Comparator<T> comparator) {
return new BinarySearch<T>() {
@Override
@SuppressWarnings( {"unchecked"})
protected int compare(int index, T element) {
return comparator.compare(list.get(index), element);
}
@Override
protected int getLastIndex() {
return list.size() - 1;
}
};
}
// ---------------------------------------------------------------- abstract
/**
* Compares element at <code>index</code> position with given object.
*/
protected abstract int compare(int index, E element);
/**
* Returns index of last element in wrapped collection.
*/
protected abstract int getLastIndex();
// ---------------------------------------------------------------- find
/**
* Finds index of given element or negative value if element is not found.
*/
public int find(E element) {
return find(element, 0, getLastIndex());
}
public int find(E element, int low) {
return find(element, low, getLastIndex());
}
/**
* Finds index of given element in inclusive index range. Returns negative
* value if element is not found.
*/
public int find(E element, int low, int high) {
while (low <= high) {
int mid = (low + high) >>> 1;
int delta = compare(mid, element);
if (delta < 0) {
low = mid + 1;
} else if (delta > 0) {
high = mid - 1;
} else {
return mid;
}
}
// not found
return -(low + 1);
}
// ---------------------------------------------------------------- first
/**
* Finds very first index of given element or negative value if element is not found.
*/
public int findFirst(E o) {
return findFirst(o, 0, getLastIndex());
}
public int findFirst(E o, int low) {
return findFirst(o, low, getLastIndex());
}
/**
* Finds very first index of given element in inclusive index range. Returns negative
* value if element is not found.
*/
public int findFirst(E o, int low, int high) {
int ndx = -1;
while (low <= high) {
int mid = (low + high) >>> 1;
int delta = compare(mid, o);
if (delta < 0) {
low = mid + 1;
} else {
if (delta == 0) {
ndx = mid;
}
high = mid - 1;
}
}
if (ndx == -1) {
return -(low + 1);
}
return ndx;
}
// ---------------------------------------------------------------- last
/**
* Finds very last index of given element or negative value if element is not found.
*/
public int findLast(E o) {
return findLast(o, 0, getLastIndex());
}
public int findLast(E o, int low) {
return findLast(o, low, getLastIndex());
}
/**
* Finds very last index of given element in inclusive index range. Returns negative
* value if element is not found.
*/
public int findLast(E o, int low, int high) {
int ndx = -1;
while (low <= high) {
int mid = (low + high) >>> 1;
int delta = compare(mid, o);
if (delta > 0) {
high = mid - 1;
} else {
if (delta == 0) {
ndx = mid;
}
low = mid + 1;
}
}
if (ndx == -1) {
return -(low + 1);
}
return ndx;
}
}
|