Justify Text - techincal interview question and answer written in Golang with many comments explaing the answer.

justify_text.go

package main

import (
	"fmt"
	"strings"
)

func main() {
	text := "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras " +
		"venenatis, quam et dapibus porttitor, nisi mauris maximus sapien, a " +
		"tempor est risus sed felis. Morbi vitae nunc iaculis, eleifend dolor " +
		"eget, congue dolor. Ut id convallis augue. Curabitur quis nisi a nulla " +
		"tempus aliquet. In non pellentesque elit, eu vulputate elit. " +
		"Suspendisse potenti. Fusce elit ipsum, dapibus sed finibus ac, " +
		"tincidunt in neque."
	maxWidth := 22

	fmt.Println(justifyText(text, maxWidth))
}

// Justifying Text: Given an input string and an maxWidth integer, return a string that is the input justified to the given maxWidth.
//
// text="The quick brown fox jumps over the lazy dog”
// maxWidth=16
// Output:
// The  quick brown
// fox  jumps  over
// the lazy dog
func justifyText(text string, maxWidth int) string {
	// Split the text into words
	words := strings.Split(text, " ")
	// Keep track of current line and previous lines
	var lines, current string
	// Iterate through each word
	for _, word := range words {
		// If the word fits, add to current
		if len(current)+len(word) <= maxWidth {
			// All words need a space after, expect for the last word
			// we will trim the space for the last word
			current += word + " "
			continue
		}
		// Otherwise, word did not fit so lets finish this line
		// Trim extra space from the last word
		current = current[:len(current)-1]
		// Distribute any extra spaces and add current line to previous lines
		lines += distributeSpaces(current, maxWidth-len(current))
		// The next iteration current line will be this word that did not fit
		current = word + " "
	}
	// return the previous lines and any current line we were working on
	return lines + current
}

// distributeSpaces will spread extra amount of whitespaces into the gaps
// between the words in s
func distributeSpaces(s string, extra int) string {
	// Nothing to do, return early
	if extra < 1 {
		return s + "\n"
	}
	// Split into tokens as it's easier to work with
	words := strings.Split(s, " ")
	// Edge case where only 1 word is on a line
	// we can just put all extra space at the end then return
	if len(words) == 1 {
		for extra > 0 {
			words[0] += " "
			extra--
		}
		return words[0] + "\n"
	}
	// calculate how many spaces between each word and any extra that dont
	// divide evenly into the gaps
	gaps := len(words) - 1
	spaces := extra + gaps
	spacePerGap, extraSpace := spaces/gaps, spaces%gaps
	// Distribute the spaces that dont fit evenly
	for i := 0; extraSpace > 0; i++ {
		words[i] += " "
		extraSpace--
	}
	// Make a tmp spacer for the whitespace that does divide evenly
	tmp := ""
	for spacePerGap > 0 {
		tmp += " "
		spacePerGap--
	}
	// Join the words with the tmp spacer
	return strings.Join(words, tmp) + "\n"
}