How I found a good opener for Wordle

package main

import (
    "bufio"
    "fmt"
    "os"
    "sort"
)

func main() {
    checkAgainstWordlist()
}

func checkAgainstWordlist() {
    lettercount := make(map[string]int)

    file, err := os.Open("Wordlist")
    if err != nil {
        panic("panic")
    }
    defer file.Close()

    scanner := bufio.NewScanner(file)
    for scanner.Scan() {

        for _, letter := range scanner.Text() {
            if val, ok := lettercount[rune2c(letter)]; ok {
                lettercount[rune2c(letter)] = val + 1
            } else {
                lettercount[rune2c(letter)] = 1
            }
        }
    }
    fmt.Println(rankByWordCount(lettercount))

    if err := scanner.Err(); err != nil {
        panic(err)
    }
}

func rune2c(r rune) string {
    return fmt.Sprintf("%c", r)
}

func rankByWordCount(wordFrequencies map[string]int) PairList {
    pl := make(PairList, len(wordFrequencies))
    i := 0
    for k, v := range wordFrequencies {
        pl[i] = Pair{k, v}
        i++
    }
    sort.Sort(sort.Reverse(pl))
    return pl
}

type Pair struct {
    Key   string
    Value int
}

type PairList []Pair

func (p PairList) Len() int {
    return len(p)
}

func (p PairList) Less(i, j int) bool {
    return p[i].Value < p[j].Value
}

func (p PairList) Swap(i, j int) {
    p[i], p[j] = p[j], p[i]
}

200: 3
201: 1
202: 0
203: 2
204: 2
205: 2
206: 2
207: 2
208: 2

200: 3 => 3
201: 1 => 3
202: 0 => 2
203: 2 => 4
204: 2 => 3
205: 2 => 2
206: 2 => 3
207: 2 => 3
208: 2 => 2