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let out_of_alphabet_character = '#';

var reg_for_the_alphabet = new RegExp(out_of_alphabet_character, "g");



function specific_revert(str) {

  str = str.replace(/(10)/g, out_of_alphabet_character);

  let temp = ;

  

  temp = str.split('');

  const backwards = ;

  const totalItems = str.length - 1;

  for (let i = totalItems; i >= 0; i--) {

    backwards.push(temp[i]);

  }

  return backwards.join('').toString().replace(reg_for_the_alphabet, '10');

}

console.log(specific_revert("10 2 3 U S A"));

console.log(specific_revert("234567891010"));

    const reverse = str => {

    	let rev = "";

    	for (let i = 0; i < str.length; i++) {

        	if (str[i] === '1' && i + 1 < str.length && str[i+1] === '0') {

            	rev = '10' + rev;

                i++;

            } else rev = str[i] + rev;

        }

        

        return rev;

    }

    

    console.log(reverse("10 2 3 U S A")); // returns A S U 3 2 10

    console.log(reverse("2345678910")); // returns 1098765432

function split(str) {

  const re = /([A-Z23456789 ]+)|(10)/g

  return str.match(re).reduce((acc, c) => {



    // if the match is 10 prepend it to the accumulator

    // otherwise reverse the match and then prepend it

    acc.unshift(c === '10' ? c : [...c].reverse().join(''));

    return acc;      

  }, ).join('');

}



console.log(split('2345678910'));

console.log(split('10 2 3 U S A'));

console.log(split('2 3 U S A10'));

String.prototype.isNumeric = function() {

  return !isNaN(parseFloat(this)) && isFinite(this);

};



function reverse(str) {

  let tokens = , len = str.length;

  while (len--) {

    let char = str.charAt(len);

    if (char.isNumeric()) {

      if (len > 0 && str.charAt(len - 1).isNumeric()) {

        let curr = parseInt(char, 10),

            next = parseInt(str.charAt(len - 1), 10);  

        if (curr === 0 && next === 1) {

          tokens.push(10);

          len--;

          continue;

        }

      }

    }

    tokens.push(char);

  }

  return tokens.join('');

}



console.log(reverse("10 2 3 U S A"));

console.log(reverse('2345678910'));

function f(s, i=0){

  if (i == s.length)

    return '';

  if (['0', '1'].includes(s[i])){

    let curr = s[i];

    while (['0', '1'].includes(s[++i]))

      curr += s[i]

    return f(s, i) + curr;

  }

  return f(s, i + 1) + s[i];

}



console.log(f('10 2 3 U S A'));

console.log(f('2345678910'));

console.log(f('USA101001'));

function reverseKeepTen(str, arr = ) {

	const tenIdx = str.indexOf('10');

  

  if (!str.length) {

  	return arr.join('');

  }

  

  if (tenIdx === -1) {

    return [...str.split('').reverse(), ...arr].join('');

  } else {

  	const digitsBefore = str.slice(0, tenIdx);

    

  	const arrBefore = digitsBefore ? [...digitsBefore.split(''), 10].reverse() : [10];

  	return reverseKeepTen(str.slice(tenIdx + 2), [...arrBefore, ...arr])

  }

};





console.log(reverseKeepTen('101234105678910')) // 109876510432110

console.log(reverseKeepTen('12341056789')) // 98765104321

console.log(reverseKeepTen('1012345')) // 5432110

console.log(reverseKeepTen('5678910')) // 1098765

console.log(reverseKeepTen('10111101')) // 11011110

function split(str) {

  let temp = ,

      bool = true;

  temp = str.split('');

  var backwards = ,

        zeroBackward = ;

  var totalItems = str.length - 1;

  for (let i = totalItems; i >= 0; i--) {

    if(temp[i] == '0' && i == totalItems) {

      zeroBackward.push(temp[i]);

      totalItems = totalItems -1;

    } else if(temp[i] != '0' && bool) {

      backwards.push(temp[i]);

      backwards = backwards.concat(zeroBackward);

      bool = false;

    } else if(!bool) {

      backwards.push(temp[i]);

    }

  }

  return backwards.join('').toString();



}

console.log(split("10 2 3 U S A"));

console.log(split("2345678910"));

console.log(split("23456789100000"));

console.log(split("234567891000001"));