# [Golang] Number letter counts - Problem 17 - Project Euler

Problem: 

If the numbers 1 to 5 are written out in words: one, two, three, four, five, then there are 3 + 3 + 5 + 4 + 4 = 19 letters used in total.

If all the numbers from 1 to 1000 (one thousand) inclusive were written out in words, how many letters would be used?

NOTE: Do not count spaces or hyphens. For example, 342 (three hundred and forty-two) contains 23 letters and 115 (one hundred and fifteen) contains 20 letters. The use of "and" when writing out numbers is in compliance with British usage.

Solution:

21124

First we convert numbers to words , and then count the letters.

Run Code on Go Playground

```package main

import (
"fmt"
)

var NumberToWord = map[int]string{
1:  "one",
2:  "two",
3:  "three",
4:  "four",
5:  "five",
6:  "six",
7:  "seven",
8:  "eight",
9:  "nine",
10: "ten",
11: "eleven",
12: "twelve",
13: "thirteen",
14: "fourteen",
15: "fifteen",
16: "sixteen",
17: "seventeen",
18: "eighteen",
19: "nineteen",
20: "twenty",
30: "thirty",
40: "forty",
50: "fifty",
60: "sixty",
70: "seventy",
80: "eighty",
90: "ninety",
}

func convert1to99(n int) (w string) {
if n < 20 {
w = NumberToWord[n]
return
}

r := n % 10
if r == 0 {
w = NumberToWord[n]
} else {
w = NumberToWord[n-r] + "-" + NumberToWord[r]
}
return
}

func convert100to999(n int) (w string) {
q := n / 100
r := n % 100
w = NumberToWord[q] + " " + "hundred"
if r == 0 {
return
} else {
w = w + " and " + convert1to99(r)
}
return
}

func Convert1to1000(n int) (w string) {
if n > 1000 || n < 1 {
panic("func Convert1to1000: n > 1000 or n < 1")
}

if n < 100 {
w = convert1to99(n)
return
}
if n == 1000 {
w = "one thousand"
return
}
w = convert100to999(n)
return
}

func CountLetter(s string) (n int) {
for _, r := range s {
if r == ' ' {
continue
}
if r == '-' {
continue
}
n++
}
return
}

func main() {
totalLetters := 0
for i := 1; i <= 1000; i++ {
totalLetters += CountLetter(Convert1to1000(i))
}
fmt.Println(totalLetters)
}
```

Tested on: Go Playground

References: