lonely_integer.go

// This is a solution implemented in Go (golang.org) for the "lonely integer" problem
// as presented here:
//
// https://www.hackerrank.com/contests/master/challenges/lonely-integer
//

package main

import (
	"bufio"
	"fmt"
	"io"
	"log"
	"strconv"
	"strings"
)

func main() {
	for _, tc := range tests {
		nums := input(strings.NewReader(tc.in))
		got := reduce(func(a, b int) int {
			return a ^ b
		}, nums...)

		fmt.Printf("Input:\n%s\n", tc.in)
		if got != tc.ans {
			fmt.Printf("[FAIL] Got %d, expected %d\n\n", got, tc.ans)
		} else {
			fmt.Printf("[OK] Got correct asnwer: %d\n\n", got)
		}
	}
}

func reduce(tr func(int, int) int, a ...int) int {
	x := 0
	for _, v := range a {
		x = tr(x, v)
	}
	return x
}

func input(in io.Reader) (out []int) {
	scn := bufio.NewScanner(in)
	// Read first line
	scn.Scan()

	// Get integer from the line
	n, err := strconv.Atoi(scn.Text())
	if err != nil {
		log.Fatal(err)
	}

	// Alloc output slice
	out = make([]int, n)

	// Read the second line
	scn.Scan()

	for i, v := range strings.SplitN(scn.Text(), " ", n) {
		if out[i], err = strconv.Atoi(v); err != nil {
			log.Fatal(err)
		}
	}

	return
}

var tests = []struct {
	in  string
	ans int
}{
	{
		"1\n1",
		1,
	},
	{
		"3\n2 1 1",
		2,
	},
	{
		"5\n0 1 3 1 0",
		3,
	},
}

Live code - https://play.golang.org/p/7obhYn3Nzz

Output:

Input:
1
1
[OK] Got correct asnwer: 1

Input:
3
2 1 1
[OK] Got correct asnwer: 2

Input:
5
0 1 3 1 0
[OK] Got correct asnwer: 3