Step by Step solution about How to resolve the algorithm Number names step by step in the Go programming language

The Go program defines a function say that converts a 64-bit integer n into its English representation. It handles negative values, numbers less than 20 (using small), tens and units (using tens), hundreds (using small and "hundred"), and large numbers by iterating through thousands, millions, billions, etc. (using illions). The program initializes slices small and tens with predefined English words and illions with number scales. Here's a breakdown of the code:

package main: Defines the main package.

import "fmt": Imports the fmt package for input/output.

func main(): The program's entry point.

It iterates through a slice of int64 values [12, 1048576, 9e18, -2, 0] and prints the English representation of each number using fmt.Println(say(n)).

func say(n int64) string: Defines a function that takes an int64 value n and returns its English representation.

It initializes t as an empty string.

If n is negative, it sets t to "negative " and makes n positive (to handle math.MinInt64).

It uses a switch statement to handle different ranges of n:

If n is less than 20, it returns the corresponding word from the small slice. If n is less than 100, it returns the tens digit (tens slice) and the units digit (small slice). If n is less than 1000, it returns the hundreds digit (small slice) and the remaining digits as a string. If n is greater than or equal to 1000, it iterates through thousands, millions, billions, etc., and appends the representation of each thousand to sx. Finally, it returns the combined string t.

The program demonstrates converting large numbers into their English representations by handling negative numbers, single digits, tens and units, hundreds, and large numbers with scales.

package main

import "fmt"

func main() {
	for _, n := range []int64{12, 1048576, 9e18, -2, 0} {
		fmt.Println(say(n))
	}
}

var small = [...]string{"zero", "one", "two", "three", "four", "five", "six",
	"seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen",
	"fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"}
var tens = [...]string{"", "", "twenty", "thirty", "forty",
	"fifty", "sixty", "seventy", "eighty", "ninety"}
var illions = [...]string{"", " thousand", " million", " billion",
	" trillion", " quadrillion", " quintillion"}

func say(n int64) string {
	var t string
	if n < 0 {
		t = "negative "
		// Note, for math.MinInt64 this leaves n negative.
		n = -n
	}
	switch {
	case n < 20:
		t += small[n]
	case n < 100:
		t += tens[n/10]
		s := n % 10
		if s > 0 {
			t += "-" + small[s]
		}
	case n < 1000:
		t += small[n/100] + " hundred"
		s := n % 100
		if s > 0 {
			t += " " + say(s)
		}
	default:
		// work right-to-left
		sx := ""
		for i := 0; n > 0; i++ {
			p := n % 1000
			n /= 1000
			if p > 0 {
				ix := say(p) + illions[i]
				if sx != "" {
					ix += " " + sx
				}
				sx = ix
			}
		}
		t += sx
	}
	return t
}