% for i in {1..100000}; do echo `od -An -N2 -l < /dev/urandom`; done > a

mode_test.go

package main

import (
	"fmt"
	"strconv"
	"bufio"
	"io"
	"os"
	"testing"
)

func setup() []int {
	res := make([]int, 0)
	f, _ := os.Open("/var/tmp/a")
	r := bufio.NewReader(f)

	for line, _, err := r.ReadLine(); err!=io.EOF; line, _, err = r.ReadLine() {
		s := string(line[:])
		i, _ := strconv.Atoi(s)
		res = append(res, i)
	}
	return res
}

func mode(arr []int) int {
	f := func(arr []int) (max_key int, max_value int) {
		for k, v := range arr {
			if max_value < v {
				max_key, max_value = k, v
			}
		}
		return max_key, max_value
	}

	_, limit := f(arr)

	r := make([]int, limit + 1)
	for _, a := range arr {
		r[a]++
	}

	mode, _ := f(r)

	return mode
}

func BenchmarkMode(b *testing.B) {
	arr := setup()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		_ = mode(arr)
	}
}

func main() {
	arr := setup()
	fmt.Println(mode(arr))
}