github.com/meulengracht/snapd@v0.0.0-20210719210640-8bde69bcc84e/strutil/set.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2019 Canonical Ltd
     5   *
     6   * This program is free software: you can redistribute it and/or modify
     7   * it under the terms of the GNU General Public License version 3 as
     8   * published by the Free Software Foundation.
     9   *
    10   * This program is distributed in the hope that it will be useful,
    11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13   * GNU General Public License for more details.
    14   *
    15   * You should have received a copy of the GNU General Public License
    16   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17   *
    18   */
    19  
    20  package strutil
    21  
    22  // OrderedSet is a set of strings that maintains the order of insertion.
    23  //
    24  // The order of putting items into the set is retained. Putting items "a", "b"
    25  // and then "a", results in order "a", "b".
    26  //
    27  // External synchronization is required for safe concurrent access.
    28  type OrderedSet struct {
    29  	positionOf map[string]int
    30  }
    31  
    32  // Items returns a slice of strings representing insertion order.
    33  //
    34  // Items is O(N) in the size of the set.
    35  func (o *OrderedSet) Items() []string {
    36  	if len(o.positionOf) == 0 {
    37  		return nil
    38  	}
    39  	items := make([]string, len(o.positionOf))
    40  	for item, idx := range o.positionOf {
    41  		items[idx] = item
    42  	}
    43  	return items
    44  }
    45  
    46  // Contains returns true if the set contains a given item.
    47  //
    48  // Contains is O(1) in the size of the set.
    49  func (o *OrderedSet) Contains(item string) bool {
    50  	_, ok := o.positionOf[item]
    51  	return ok
    52  }
    53  
    54  // IndexOf returns the position of an item in the set.
    55  func (o *OrderedSet) IndexOf(item string) (idx int, ok bool) {
    56  	idx, ok = o.positionOf[item]
    57  	return idx, ok
    58  }
    59  
    60  // Put adds an item into the set.
    61  //
    62  // If the item was not present then it is stored and ordered after all existing
    63  // elements. If the item was already present its position is not changed.
    64  //
    65  // Put is O(1) in the size of the set.
    66  func (o *OrderedSet) Put(item string) {
    67  	if o.positionOf == nil {
    68  		o.positionOf = make(map[string]int)
    69  	}
    70  
    71  	if _, ok := o.positionOf[item]; ok {
    72  		return
    73  	}
    74  
    75  	o.positionOf[item] = len(o.positionOf)
    76  }
    77  
    78  // Size returns the number of elements in the set.
    79  func (o *OrderedSet) Size() int {
    80  	return len(o.positionOf)
    81  }