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82 lines
2.2 KiB
Go
82 lines
2.2 KiB
Go
// -*- Mode: Go; indent-tabs-mode: t -*-
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/*
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* Copyright (C) 2019 Canonical Ltd
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 3 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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package strutil
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// OrderedSet is a set of strings that maintains the order of insertion.
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//
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// The order of putting items into the set is retained. Putting items "a", "b"
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// and then "a", results in order "a", "b".
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//
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// External synchronization is required for safe concurrent access.
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type OrderedSet struct {
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positionOf map[string]int
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}
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// Items returns a slice of strings representing insertion order.
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//
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// Items is O(N) in the size of the set.
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func (o *OrderedSet) Items() []string {
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if len(o.positionOf) == 0 {
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return nil
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}
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items := make([]string, len(o.positionOf))
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for item, idx := range o.positionOf {
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items[idx] = item
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}
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return items
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}
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// Contains returns true if the set contains a given item.
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//
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// Contains is O(1) in the size of the set.
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func (o *OrderedSet) Contains(item string) bool {
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_, ok := o.positionOf[item]
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return ok
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}
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// IndexOf returns the position of an item in the set.
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func (o *OrderedSet) IndexOf(item string) (idx int, ok bool) {
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idx, ok = o.positionOf[item]
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return idx, ok
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}
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// Put adds an item into the set.
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//
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// If the item was not present then it is stored and ordered after all existing
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// elements. If the item was already present its position is not changed.
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//
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// Put is O(1) in the size of the set.
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func (o *OrderedSet) Put(item string) {
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if o.positionOf == nil {
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o.positionOf = make(map[string]int)
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}
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if _, ok := o.positionOf[item]; ok {
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return
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}
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o.positionOf[item] = len(o.positionOf)
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}
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// Size returns the number of elements in the set.
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func (o *OrderedSet) Size() int {
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return len(o.positionOf)
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}
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