74 lines
1.4 KiB
Go
74 lines
1.4 KiB
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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// See page 165.
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// Package intset provides a set of integers based on a bit vector.
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package intset
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import (
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"bytes"
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"fmt"
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)
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//!+intset
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// An IntSet is a set of small non-negative integers.
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// Its zero value represents the empty set.
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type IntSet struct {
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words []uint64
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}
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// Has reports whether the set contains the non-negative value x.
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func (s *IntSet) Has(x int) bool {
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word, bit := x/64, uint(x%64)
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return word < len(s.words) && s.words[word]&(1<<bit) != 0
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}
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// Add adds the non-negative value x to the set.
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func (s *IntSet) Add(x int) {
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word, bit := x/64, uint(x%64)
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for word >= len(s.words) {
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s.words = append(s.words, 0)
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}
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s.words[word] |= 1 << bit
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}
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// UnionWith sets s to the union of s and t.
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func (s *IntSet) UnionWith(t *IntSet) {
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for i, tword := range t.words {
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if i < len(s.words) {
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s.words[i] |= tword
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} else {
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s.words = append(s.words, tword)
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}
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}
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}
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//!-intset
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//!+string
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// String returns the set as a string of the form "{1 2 3}".
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func (s *IntSet) String() string {
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var buf bytes.Buffer
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buf.WriteByte('{')
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for i, word := range s.words {
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if word == 0 {
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continue
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}
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for j := 0; j < 64; j++ {
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if word&(1<<uint(j)) != 0 {
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if buf.Len() > len("{") {
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buf.WriteByte(' ')
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}
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fmt.Fprintf(&buf, "%d", 64*i+j)
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}
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}
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}
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buf.WriteByte('}')
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return buf.String()
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}
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//!-string
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