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With inspiration from other libraries
// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html#License
/*
**********************************************************************
* Copyright (c) 2002-2010, International Business Machines
* Corporation and others. All Rights Reserved.
**********************************************************************
* Author: M. Davis
* Created: December 2002 (moved from UnicodeSet)
* Since: ICU 2.4
**********************************************************************
*/
package com.ibm.icu.impl;
import java.util.Iterator;
import java.util.SortedSet;
import java.util.TreeSet;
/**
* Computationally efficient determination of the relationship between
* two SortedSets.
*/
public class SortedSetRelation {
/**
* The relationship between two sets A and B can be determined by looking at:
* A - B
* A & B (intersection)
* B - A
* These are represented by a set of bits.
* Bit 2 is true if A - B is not empty
* Bit 1 is true if A & B is not empty
* BIT 0 is true if B - A is not empty
*/
public static final int
A_NOT_B = 4,
A_AND_B = 2,
B_NOT_A = 1;
/**
* There are 8 combinations of the relationship bits. These correspond to
* the filters (combinations of allowed bits) in hasRelation. They also
* correspond to the modification functions, listed in comments.
*/
public static final int
ANY = A_NOT_B | A_AND_B | B_NOT_A, // union, addAll
CONTAINS = A_NOT_B | A_AND_B, // A (unnecessary)
DISJOINT = A_NOT_B | B_NOT_A, // A xor B, missing Java function
ISCONTAINED = A_AND_B | B_NOT_A, // B (unnecessary)
NO_B = A_NOT_B, // A setDiff B, removeAll
EQUALS = A_AND_B, // A intersect B, retainAll
NO_A = B_NOT_A, // B setDiff A, removeAll
NONE = 0, // null (unnecessary)
ADDALL = ANY, // union, addAll
A = CONTAINS, // A (unnecessary)
COMPLEMENTALL = DISJOINT, // A xor B, missing Java function
B = ISCONTAINED, // B (unnecessary)
REMOVEALL = NO_B, // A setDiff B, removeAll
RETAINALL = EQUALS, // A intersect B, retainAll
B_REMOVEALL = NO_A; // B setDiff A, removeAll
/**
* Utility that could be on SortedSet. Faster implementation than
* what is in Java for doing contains, equals, etc.
* @param a first set
* @param allow filter, using ANY, CONTAINS, etc.
* @param b second set
* @return whether the filter relationship is true or not.
*/
public static > boolean hasRelation(SortedSet a, int allow, SortedSet b) {
if (allow < NONE || allow > ANY) {
throw new IllegalArgumentException("Relation " + allow + " out of range");
}
// extract filter conditions
// these are the ALLOWED conditions Set
boolean anb = (allow & A_NOT_B) != 0;
boolean ab = (allow & A_AND_B) != 0;
boolean bna = (allow & B_NOT_A) != 0;
// quick check on sizes
switch(allow) {
case CONTAINS: if (a.size() < b.size()) return false; break;
case ISCONTAINED: if (a.size() > b.size()) return false; break;
case EQUALS: if (a.size() != b.size()) return false; break;
}
// check for null sets
if (a.size() == 0) {
if (b.size() == 0) return true;
return bna;
} else if (b.size() == 0) {
return anb;
}
// pick up first strings, and start comparing
Iterator ait = a.iterator();
Iterator bit = b.iterator();
T aa = ait.next();
T bb = bit.next();
while (true) {
int comp = aa.compareTo(bb);
if (comp == 0) {
if (!ab) return false;
if (!ait.hasNext()) {
if (!bit.hasNext()) return true;
return bna;
} else if (!bit.hasNext()) {
return anb;
}
aa = ait.next();
bb = bit.next();
} else if (comp < 0) {
if (!anb) return false;
if (!ait.hasNext()) {
return bna;
}
aa = ait.next();
} else {
if (!bna) return false;
if (!bit.hasNext()) {
return anb;
}
bb = bit.next();
}
}
}
/**
* Utility that could be on SortedSet. Allows faster implementation than
* what is in Java for doing addAll, removeAll, retainAll, (complementAll).
* @param a first set
* @param relation the relation filter, using ANY, CONTAINS, etc.
* @param b second set
* @return the new set
*/
public static > SortedSet doOperation(SortedSet a, int relation, SortedSet b) {
// TODO: optimize this as above
TreeSet temp;
switch (relation) {
case ADDALL:
a.addAll(b);
return a;
case A:
return a; // no action
case B:
a.clear();
a.addAll(b);
return a;
case REMOVEALL:
a.removeAll(b);
return a;
case RETAINALL:
a.retainAll(b);
return a;
// the following is the only case not really supported by Java
// although all could be optimized
case COMPLEMENTALL:
temp = new TreeSet(b);
temp.removeAll(a);
a.removeAll(b);
a.addAll(temp);
return a;
case B_REMOVEALL:
temp = new TreeSet(b);
temp.removeAll(a);
a.clear();
a.addAll(temp);
return a;
case NONE:
a.clear();
return a;
default:
throw new IllegalArgumentException("Relation " + relation + " out of range");
}
}
}