Move string capital letters to front while maintaining the order (JavaScript)

Question

This is my first post so I hope im doing this correctly.

I am taking a coding class and we were asked to make a piece of code that will ask for the input of a phrase, and will return in the console that phrase with the capital letters moved to the front, but still in the same order. Then print to the console this reordered phrase. (We aren't allowed to use arrays) For example: Inputting "HeLLoTherE" would return "HLLTEeoher"

However the problem is im having issues understanding how to write this code. How can I make the code select these capital letters and move them to the front? using .toUpperCase()? How can i make that select the letter and move it in front of the rest? If someone could show me an example of how this is done and explain it a little i would greatly appreciate it :)

Answer 1

You might just start with a the most straight forward algorithm to get something working.

let value = "HeLLoTherE";
let result = "";

for (let char of value) {
  if (char >= "A" && char <= "Z") {
    result += char;
  }
}

for (let char of value) {
  if (char >= "a" && char <= "z") {
    result += char;
  }
}

console.log(result);

You could then consolidate the 2 loops by combining the conditions.

let value = "HeLLoTherE";
let upper = "";
let lower = "";

for (let char of value) {
  if (char >= "A" && char <= "Z") {
    upper += char;
  } else if (char >= "a" && char <= "z") {
    lower += char;
  }  
}

console.log(upper + lower);

Another way of solving this would be to use regex.

var value = "HeLLoTherE";
var upper = value.replace(/[^A-Z]*/g, "");
var lower = value.replace(/[^a-z]*/g, "");

console.log(upper + lower);

Answer 2

Well, you are not able to use arrays, which makes it a little bit difficult, however you can still do sommething.

Although I'm using a for loop, I'm not actually using arrays. Since strings allows the [] operator, you can use an index to select each character of the string and check if it's lowercase or uppercase.

In addition, you said you need to mantain the order of uppercase letters, so you couldn't just do newStr = upper + newStr, because it would revert the original order. So, I used the string.prototype.substring() to insert the uppercase character where it should be.

const str = "HeLLoTherE";

const moveUpperToFront = (target) => {
  // Strings are immutable in js, so you cannot move one character
  // to the front without using a new string.
  let newStr = "";
  // Number of uppercase letters that appeared.
  // It's necessary because you need to mantain the original order
  let upperNumber = 0;
  // Iterate each character from beginning
  for (let i = 0; i < str.length; ++i) {
    // Is there an uppercase letter?
    if (str[i].charCodeAt() >= 65 && str[i].charCodeAt() <= 90) {
      newStr =
        newStr.substring(0, upperNumber) +
        str[i] +
        newStr.substring(upperNumber, newStr.length);

      ++upperNumber;
    }
    // No uppercase letter?
    else
      newStr += str[i];
  }
  return newStr;
};

console.log(moveUpperToFront(str));