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線形探索ではなく2分木探索した方がいいサイズってどれくらいなのか

More than 3 years have passed since last update.

ふと思ったので調べてみた

適当にやっているだけなので真に受けないでください

catatsuy/linear_binary_compare

package main

import (
    "math/rand"
    "testing"
    "time"
)

const (
    Size = 75
)

func BenchmarkLinearSearch(b *testing.B) {
    b.StopTimer()

    lists := make([]int, 0)
    for i := 0; i < Size; i++ {
        lists = append(lists, i)
    }
    rand.Seed(time.Now().UnixNano())

    b.StartTimer()

    for i := 0; i < b.N; i++ {
        target := rand.Intn(len(lists))
        for _, v := range lists {
            if target == v {
                break
            }
        }
    }
}

func BenchmarkBinarySearch(b *testing.B) {
    b.StopTimer()

    lists := make([]int, 0)
    for i := 0; i < Size; i++ {
        lists = append(lists, i)
    }
    rand.Seed(time.Now().UnixNano())

    b.StartTimer()

    for i := 0; i < b.N; i++ {
        start, end := 0, len(lists)-1
        target := rand.Intn(len(lists))
        for start <= end {
            pivot := (start + end) / 2
            if lists[pivot] < target {
                start = pivot + 1
            } else if lists[pivot] > target {
                end = pivot - 1
            } else {
                break
            }
        }
    }
}

手元のMacBook Proでは75くらいで前後し始めた。それより小さいサイズでは線形探索の方が早い。

こういうときにGoを使うの、サクッとかけるし正確なベンチが取れそうな気がする。

それとこれはあくまでも平均で、最悪実行時間は線形探索の方が遅いはずなので実際はこれよりも小さいサイズでも2分木探索の方が良いはず。

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