var str = `/* * Function to chop a string in half. */ public static string chop(string input) { if (input == null || input.isEmpty()) { return input; } if (input.length() % 2 == 1) { return "cannot chop an odd-length string in half"; } return input.substring(input.length() / 2); }`
// var str ="you say yes, I say no you say stop and I say go go go"
      // "you say yes, I $1 no $0 $1 stop and $3 $1 go $12 $12"

var map = {};

str = str.split('');
let point = -1;
let wordCounter = 1;
for (let x = 0; x < str.length; x++) {
  if (str[x].charCodeAt(0) >= "A".charCodeAt(0) && str[x].charCodeAt(0) <= "z".charCodeAt(0)) {
    if (point === -1) {
      point = x;
    }
  } else {
    if (point !== -1) {
      let word = str.slice(point, x).join('');
      // console.log(word)
      if (map[word]) {
        str.splice(point, x - point, `$${map[word] - 1}`);
        x = point + 1;
      } else {
        map[word] = wordCounter;
      }
      wordCounter++;
      point = -1;
    }
  }
}
if (point !== -1) {
  let word = str.slice(point, str.length).join('');
  // console.log(word)
  if (map[word]) {
    str.splice(point, str.length - point, `$${map[word] - 1}`);
    str.length = point + 1;
  } else {
    map[word] = wordCounter;
  }
  wordCounter++;
  point = -1;
}

console.log(str.join(''))