I implemented my algorithm for checking if the string passed in is unique. I feel like my algorithm is correct, but obviously in certain cases it gives the wrong results. Why?

function isUnique(str) {
  let sortedArr = str.split('').sort();
  for (let [i, char] of sortedArr.entries()) {
    if (char === sortedArr[i + 1]) {
      return false
    } else {
      return true
    }
  }
}

console.log(isUnique('heloworld')) // true

I implemented my algorithm for checking if the string passed in is unique. I feel like my algorithm is correct, but obviously in certain cases it gives the wrong results. Why?

function isUnique(str) {
  let sortedArr = str.split('').sort();
  for (let [i, char] of sortedArr.entries()) {
    if (char === sortedArr[i + 1]) {
      return false
    } else {
      return true
    }
  }
}

console.log(isUnique('heloworld')) // true

• javascript

• FWIW: function noDuplicatedChars() { const chars = new Set(); for (let c of str) { if (chars.has(c)) return false; chars.add(c);} return true; } is a faster alternative. – Frax Commented Apr 3, 2019 at 5:55

2 Answers 2

return immediately terminates the function, so only the first iteration if your for loop will ever run. Instead, you should check for whether all characters are unique (if not, return false inside the loop), else return true after the end of the loop:

function isUnique(str) {
  let sortedArr = str.split('').sort();
  for(let [i,char] of sortedArr.entries()) {
    if(char === sortedArr[i + 1]) {
      return false
    }
  }
  return true
}

console.log(isUnique('heloworld'))

But it would probably be a lot easier to use a Set, and see if its size is equal to the length of the string:

function isUnique(str) {
  return new Set(str).size === str.length;
}

console.log(isUnique('heloworld'))
console.log(isUnique('abc'))

See comment, thanks Patrick: if you need to account for characters composed of multiple UCS-2 code points (