Fix trie Keys method

Fixes #20

trie/trie.go

@@ -161,8 +161,5 @@ func (t *Trie[V]) collect(x *node[V], prefix string, queue []string) []string {
 		queue = append(queue, prefix+string(x.c))
 	}
 	queue = t.collect(x.mid, prefix+string(x.c), queue)
-	if len(prefix) > 0 {
-		prefix = prefix[:len(prefix)-1]
-	}
 	return t.collect(x.right, prefix, queue)
 }

trie/trie_test.go

@@ -3,6 +3,7 @@ package trie_test
 import (
 	"fmt"
 	"math/rand"
+	"sort"
 	"testing"
 
 	"github.com/zyedidia/generic/trie"
@@ -19,7 +20,9 @@ func randstring(n int) string {
 }
 
 func checkeq(tr *trie.Trie[int], m map[string]int, t *testing.T) {
+	keys := make([]string, 0, len(m))
 	for k, v := range m {
+		keys = append(keys, k)
 		tv, ok := tr.Get(k)
 		if !ok {
 			t.Fatalf("%v should exist", k)
@@ -28,6 +31,13 @@ func checkeq(tr *trie.Trie[int], m map[string]int, t *testing.T) {
 			t.Fatalf("%v != %v, key: %v", tv, v, k)
 		}
 	}
+	trieKeys := tr.Keys()
+	sort.Strings(keys)
+	for i := range keys {
+		if keys[i] != trieKeys[i] {
+			t.Fatalf("%d, %s != %s", i, keys, trieKeys)
+		}
+	}
 }
 
 func TestCrossCheck(t *testing.T) {
@@ -59,6 +69,17 @@ func TestCrossCheck(t *testing.T) {
 	}
 }
 
+func TestKeys(t *testing.T) {
+	tr := trie.New[int]()
+	tr.Put("topic1", 1)
+	tr.Put("topic2", 2)
+
+	keys := tr.Keys()
+	if len(keys) != 2 || keys[0] != "topic1" || keys[1] != "topic2" {
+		t.Fatal(keys)
+	}
+}
+
 func Example() {
 	tr := trie.New[int]()
 	tr.Put("foo", 1)