Code kata. https://forum.lowyat.net/index.php?showtopic=3571866&view=findpost&p=75952192

friends.go

package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"regexp"
	"strconv"
)

func doCluster(input io.Reader) {
	re, _ := regexp.Compile("(?i)[0-9]+")

	scanner := bufio.NewScanner(input) // was os.Stdin
	scanner.Scan()
	// I'm getting lazy
	scannedText := scanner.Text()
	words := re.FindAllStringSubmatch(scannedText, -1)
	//maxFriends, _ := strconv.Atoi(words[0][0])
	maxPairs, _ := strconv.Atoi(words[1][0])

	clusters := make([][]int, 0)
	clusterMap := make(map[int]int, 0)
	for i := 0; i < maxPairs; i++ {
		scanner.Scan()
		scannedText := scanner.Text()
		words = re.FindAllStringSubmatch(scannedText, -1)
		one, _ := strconv.Atoi(words[0][0])
		two, _ := strconv.Atoi(words[1][0])

		oneIdx, oneInCluster := clusterMap[one]
		twoIdx, twoInCluser := clusterMap[two]

		if !oneInCluster && !twoInCluser {
			newCluster := []int{one, two}
			clusters = append(clusters, newCluster)
			clusterMap[one] = len(clusters) - 1
			clusterMap[two] = len(clusters) - 1
		} else if oneInCluster && !twoInCluser {
			clusters[oneIdx] = append(clusters[oneIdx], two)
			clusterMap[two] = oneIdx
		} else if twoInCluser && !oneInCluster {
			clusters[twoIdx] = append(clusters[twoIdx], one)
			clusterMap[one] = twoIdx
		}
	}
	maxClusterLength := 0
	for _, cluster := range clusters {
		if len(cluster) > maxClusterLength {
			maxClusterLength = len(cluster)
		}
	}
	fmt.Println(maxClusterLength)
}

func main() {
	input := bytes.NewBufferString(`5 3
1 2
3 2
4 5`)
	doCluster(input)
	input = bytes.NewBufferString(`10 12
1 2
3 1
3 4
5 4
3 5
4 6
5 2
2 1
7 10
1 2
9 10
8 9`)
	doCluster(input)
}