Count Possible Decodings of a digit sequence into letters in Go (Golang)

Table of Contents

Overview

Let’s say we have below number to letter mapping

'A' -> "1"
'B' -> "2"
...
'Z' -> "26"

The objective is to count the number of possible decoding of a given digit sequence

Examples

Input: '15'
Output: 2
15 can be decoded as "AE" or "O"

Program

Here is the program for the same.

package main
import (
"fmt"
"strconv"
)
func numDecodings(s string) int {
runeArray := []rune(s)
length := len(runeArray)
if length == 0 {
return 0
}
if string(runeArray[0]) == "0" {
return 0
}
numwaysArray := make([]int, length)
numwaysArray[0] = 1
if length == 1 {
return numwaysArray[0]
}
secondDigit := string(runeArray[0:2])
num, _ := strconv.Atoi(secondDigit)
if num > 10 && num <= 19 {
numwaysArray[1] = 2
} else if num > 20 && num <= 26 {
numwaysArray[1] = 2
} else if num == 10 || num == 20 {
numwaysArray[1] = 1
} else if num%10 == 0 {
numwaysArray[1] = 0
} else {
numwaysArray[1] = 1
}
for i := 2; i < length; i++ {
firstDigit := string(runeArray[i])
if firstDigit != "0" {
numwaysArray[i] = numwaysArray[i] + numwaysArray[i-1]
}
secondDigit := string(runeArray[i-1 : i+1])
fmt.Println(i)
fmt.Println(secondDigit)
num, _ := strconv.Atoi(secondDigit)
if num >= 10 && num <= 26 {
numwaysArray[i] = numwaysArray[i] + numwaysArray[i-2]
}
}
return numwaysArray[length-1]
}
func main() {
output := numDecodings("15")
fmt.Println(output)
}

Output

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