Created
January 22, 2019 18:11
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Three algorithms to do filter input array of integers in place.
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package main | |
import ( | |
"reflect" | |
"sort" | |
"testing" | |
) | |
func filterByAppend(input []int) []int { | |
output := input[:0] | |
for _, num := range input { | |
if num != 0 { | |
output = append(output, num) | |
} | |
} | |
return output | |
} | |
func filterBySwap(input []int) []int { | |
var zero int | |
for i, num := range input { | |
if num != 0 { | |
input[i], input[zero] = input[zero], input[i] | |
zero++ | |
} | |
} | |
return input[:zero] | |
} | |
func filterBySort(input []int) []int { | |
var border int | |
sort.Ints(input) | |
for i, num := range input { | |
if num != 0 { | |
border = i | |
break | |
} | |
} | |
return input[border:] | |
} | |
func TestFilter(t *testing.T) { | |
tests := []struct { | |
name string | |
algorithm func([]int) []int | |
input, expected []int | |
}{ | |
{"filter by append", filterByAppend, []int{0, 1, 0, 0, 2, 3, 4, 0, 5, 0}, []int{1, 2, 3, 4, 5}}, | |
{"filter by swap", filterBySwap, []int{0, 1, 0, 0, 2, 3, 4, 0, 5, 0}, []int{1, 2, 3, 4, 5}}, | |
{"filter by sort", filterBySort, []int{0, 1, 0, 0, 2, 3, 4, 0, 5, 0}, []int{1, 2, 3, 4, 5}}, | |
} | |
for _, test := range tests { | |
tc := test | |
t.Run(test.name, func(t *testing.T) { | |
tc.input = tc.algorithm(tc.input) | |
if !reflect.DeepEqual(tc.input, tc.expected) { | |
t.Errorf("expected %+v, obtained %+v", tc.expected, tc.input) | |
} | |
}) | |
} | |
} | |
// goos: darwin | |
// goarch: amd64 | |
// BenchmarkFilter/filter_by_append-4 50000000 20.9 ns/op 0 B/op 0 allocs/op | |
// BenchmarkFilter/filter_by_swap-4 100000000 20.5 ns/op 0 B/op 0 allocs/op | |
// BenchmarkFilter/filter_by_sort-4 10000000 185 ns/op 32 B/op 1 allocs/op | |
func BenchmarkFilter(b *testing.B) { | |
benchmarks := []struct { | |
name string | |
algorithm func([]int) []int | |
input []int | |
}{ | |
{"filter by append", filterByAppend, []int{0, 1, 0, 0, 2, 3, 4, 0, 5, 0}}, | |
{"filter by swap", filterBySwap, []int{0, 1, 0, 0, 2, 3, 4, 0, 5, 0}}, | |
{"filter by sort", filterBySort, []int{0, 1, 0, 0, 2, 3, 4, 0, 5, 0}}, | |
} | |
for _, bm := range benchmarks { | |
tc := bm | |
b.Run(bm.name, func(b *testing.B) { | |
copied := make([]int, len(tc.input)) | |
b.ReportAllocs() | |
b.ResetTimer() | |
for i := 0; i < b.N; i++ { | |
copy(copied, tc.input) | |
_ = tc.algorithm(tc.input) | |
} | |
}) | |
} | |
} |
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