Since there will always be an existing solution less than ~1000~, we can simply try and put each number from the interval ~[1, 999]~ in the sentence and check whether it is the possible solution. For a sentence with the number ~x~ in it to be valid, the following condition must be met:

length of the name of number ~x~ ~+~ sum of word length in the sentence ~= x~

Now the only problem is to create a function which will determine the names of numbers. We can do this in the following way:

• create three arrays, ~special[]~, ~tens[]~, ~hundreds[]~
• the array ~special~ is going to consist of names of numbers ~1~ to ~19~, e.g. ~special[11]~ is going to be eleven
• the array ~tens~ is going to consist of names of tens, e.g. ~tens[7]~ is going to be seventy
• identically, the array ~hundreds~ is going to consist of names of hundreds, e.g. ~hundreds[3]~ is going to be threehundred
• now we implement naming the numbers as described in the task

Pseudocode:

name(x)
  answer = ''
  if the hundreds' digit of x is not 0:
    answer = answer + hundreds[hundreds' digit of x]
  remove the hundreds' digit from x
  if x is from the interval [1, 19]:
    answer = answer + special[x]
  else:
    if the tens' digit of x is not 0:
      answer = answer + tens[tens' digit of x]
    if the single digit of x is not 0:
      answer = answer + single[single digit of x]