code.org phone screen

_prompt.js

/*
Justify a string

Given an input string of words and spaces, and a desired line length n which is greater than or equal 
to the length of the input string, output a string that differs only in whitespace from the original
string which meets the following requirements:
 - the new string has length n
 - no spaces before the first word
 - no spaces after the last word
 - the number of spaces between a pair of consecutive words differs by no more than 1 from the 
   number of spaces between any other pair of consecutive words.

For example, given the following inputs (using '-' instead of spaces for clarity):
str = "a-b-c-d" // length 7
n = 9 // length to justify the string to

The following outputs would be acceptable:
"a--b--c-d"
"a--b-c--d"

justify("a-b-c-d", 9) --> "a--b--c-d" (length 9)

However the following output would be unacceptable, because the number of spaces between words differs by more than 1:
"a---b-c-d"

function justify(str, n) {...}

assumptions:
n >= str.length
str does not start or end in spaces
*/

justify.js

const SPACE = ' ';
function justify(str, target_length) {
  const words = str.split(SPACE);
  const spaces = [];
  const { space, characters } = count(str);

  const calculated_spaces = target_length - characters;
  const multiplier = space > 0 ? Math.floor(calculated_spaces / space) : 0;
  let remainder = calculated_spaces - (multiplier * space);

  if (multiplier < 1) {
    return str;
  }

  for (let i = 0; i < words.length - 1; i++) {
    let repeat_count = multiplier;
    if (remainder > 0) {
      repeat_count++;
      remainder--;
    }
    spaces.push(repeat(SPACE, repeat_count));
  }

  const justified = [];
  for (let word of words) {
    justified.push(word);
    if (spaces.length > 0) {
      justified.push(spaces.shift());
    }
  }
  return justified.join('');
}

function count(str) {
  let space_count = 0;
  let char_count = 0;
  for (let i = 0; i < str.length; i++) {
    if (str.charAt(i) === SPACE) {
      space_count++;
    } else {
      char_count++;
    }
  }
  return {
    space: space_count,
    characters: char_count,
  };
}

function repeat(str, count) {
  let output = '';
  for (let i = 0; i < count; i++) {
    output += str;
  }
  return output;
}

function test({ str, length }, expected) {
  const actual = justify(str, length);
  if (actual === expected) {
    console.log(`  [ok]: '${actual}' (length: ${length})`);
  } else {
    console.log(`[fail] '${actual}' != '${expected}'`);
  }
}

console.log('test');
test({ str: 'a b c d', length: 9 }, 'a  b  c d');
test({ str: 'a b c', length: 7 }, 'a  b  c');
test({ str: 'hello', length: 7 }, 'hello');
test({ str: 'hello', length: 5 }, 'hello');
test({ str: '1  2 3  4', length: 9 }, '1  2 3  4');
test({ str: '1 2 3 4', length: 10 }, '1  2  3  4');
test({ str: '1 2 3 4', length: 11 }, '1   2  3  4');
test({ str: '11 22', length: 10 }, '11      22');
test({ str: '11 22', length: 6 }, '11  22');
test({ str: '1 1 2  2', length: 9 }, '1  1 2  2');