util: Add disjoint package to implement a union find datastructure

This is a fascinating, and incredibly simple data structure. I hope I
can end up using it for more than just type unification!

Thanks to Sam who taught me about its existence.

util/disjoint/disjoint_test.go

@@ -0,0 +1,96 @@
+// Mgmt
+// Copyright (C) 2013-2024+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+//go:build !root
+
+package disjoint
+
+import (
+	"sort"
+	"testing"
+)
+
+func TestUnionFind0(t *testing.T) {
+	s1 := NewElem[bool]()
+	s2 := NewElem[bool]()
+	s3 := NewElem[bool]()
+
+	s1.Union(s2)
+
+	f1 := s1.Find()
+	f2 := s2.Find()
+	f3 := s3.Find()
+
+	if f1 != f2 || !IsConnected(f1, f2) {
+		t.Errorf("f1 and f2 are not in the same set")
+	}
+	if f2 == f3 || IsConnected(f2, f3) {
+		t.Errorf("f1 and f2 should not be in the same set")
+	}
+}
+
+func TestMerge0(t *testing.T) {
+	s1 := NewElem[[]string]()
+	s1.Data = []string{"a"}
+	s2 := NewElem[[]string]()
+	s2.Data = []string{"b"}
+	s3 := NewElem[[]string]()
+	s3.Data = []string{"c"}
+
+	//s1.Union(s2)
+	//s2.Union(s3)
+	merge := func(a, b []string) ([]string, error) {
+		t.Logf("merge: `%s` and `%s`", a, b)
+		c := []string{}
+		c = append(c, a...)
+		c = append(c, b...)
+		return c, nil
+	}
+	if err := UnsafeMerge(s1, s2, merge); err != nil {
+		t.Errorf("merge error: %v", err)
+		return
+	}
+
+	// If this is UnsafeMerge, we should correctly fail!
+	if err := Merge(s2, s3, merge); err != nil {
+		t.Errorf("merge error: %v", err)
+		return
+	}
+
+	x := s3.Find().Data
+	sort.Strings(x)
+
+	// TODO: use compare in golang 1.21
+	//if !slices.Compare(x, []string{"a", "b", "c"}) {
+	//	t.Errorf("wrong data")
+	//}
+	if x[0] != "a" || x[1] != "b" || x[2] != "c" {
+		t.Errorf("wrong data, got: %v", x)
+	}
+}