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Check for characters in a string being unique

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8

1

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

share|improve this question

edited Apr 3 at 11:13

Peter Mortensen

14k1987114

asked Apr 3 at 5:35

user3763875user3763875

745

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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
  Apr 3 at 5:55
  

  
  
  
  

add a comment | 

8

1

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

share|improve this question

edited Apr 3 at 11:13

Peter Mortensen

14k1987114

asked Apr 3 at 5:35

user3763875user3763875

745

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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
  Apr 3 at 5:55
  

  
  
  
  

add a comment | 

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

share|improve this question

edited Apr 3 at 11:13

Peter Mortensen

14k1987114

asked Apr 3 at 5:35

user3763875user3763875

745

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

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

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

share|improve this question

edited Apr 3 at 11:13

Peter Mortensen

14k1987114

asked Apr 3 at 5:35

user3763875user3763875

745

share|improve this question

edited Apr 3 at 11:13

Peter Mortensen

14k1987114

asked Apr 3 at 5:35

user3763875user3763875

745

edited Apr 3 at 11:13

Peter Mortensen

14k1987114

edited Apr 3 at 11:13

Peter Mortensen

14k1987114

asked Apr 3 at 5:35

user3763875user3763875

745

asked Apr 3 at 5:35

user3763875user3763875

745

2 Answers
2

active

oldest

votes

25

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 (𝟙𝟚𝟛😎😜🙃 etc), call the string iterator and check how many items it returns, which can be done with spread or Array.from (because otherwise, str.length won't evaluate to the right number of individual characters):

function isUnique(str) 
 return new Set(str).size === [...str].length;


console.log(isUnique('😜'));
console.log(isUnique('😜😜'));

share|improve this answer

edited Apr 3 at 6:03

Patrick Roberts

21.3k33777

answered Apr 3 at 5:37

CertainPerformanceCertainPerformance

101k166292

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Not sure if this matters but for multi-unit code points you get the wrong answer, e.g. isUnique('😀😁') === false
  
  – Patrick Roberts
  Apr 3 at 5:42
  
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  The fix is relatively simple though: return new Set(str).size === Array.from(str).length;
  
  – Patrick Roberts
  Apr 3 at 5:50
  

  
  
  
  

add a comment | 

0

Only first iteration in your for loop is run (because you always execute 'return'). Instead you can use following code

function isUnique(str, t=) 
 
 return ![...str].some(c=> t[c]=c in t)


console.log('heloworld =>',isUnique('heloworld'));
console.log('helo =>',isUnique('helo'));

share|improve this answer

edited Apr 3 at 8:07

answered Apr 3 at 5:52

Kamil KiełczewskiKamil Kiełczewski

14.5k87497

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why is r a parameter?
  
  – JollyJoker
  Apr 3 at 8:01
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  r (I rename it to t) is temporary hash map (define in tricky way as default param)
  
  – Kamil Kiełczewski
  Apr 3 at 8:07
  
  

  
  
  
  

add a comment | 

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25

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 (𝟙𝟚𝟛😎😜🙃 etc), call the string iterator and check how many items it returns, which can be done with spread or Array.from (because otherwise, str.length won't evaluate to the right number of individual characters):

function isUnique(str) 
 return new Set(str).size === [...str].length;


console.log(isUnique('😜'));
console.log(isUnique('😜😜'));

share|improve this answer

edited Apr 3 at 6:03

Patrick Roberts

21.3k33777

answered Apr 3 at 5:37

CertainPerformanceCertainPerformance

101k166292

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Not sure if this matters but for multi-unit code points you get the wrong answer, e.g. isUnique('😀😁') === false
  
  – Patrick Roberts
  Apr 3 at 5:42
  
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  The fix is relatively simple though: return new Set(str).size === Array.from(str).length;
  
  – Patrick Roberts
  Apr 3 at 5:50
  

  
  
  
  

add a comment | 

25

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 (𝟙𝟚𝟛😎😜🙃 etc), call the string iterator and check how many items it returns, which can be done with spread or Array.from (because otherwise, str.length won't evaluate to the right number of individual characters):

function isUnique(str) 
 return new Set(str).size === [...str].length;


console.log(isUnique('😜'));
console.log(isUnique('😜😜'));

share|improve this answer

edited Apr 3 at 6:03

Patrick Roberts

21.3k33777

answered Apr 3 at 5:37

CertainPerformanceCertainPerformance

101k166292

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Not sure if this matters but for multi-unit code points you get the wrong answer, e.g. isUnique('😀😁') === false
  
  – Patrick Roberts
  Apr 3 at 5:42
  
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  The fix is relatively simple though: return new Set(str).size === Array.from(str).length;
  
  – Patrick Roberts
  Apr 3 at 5:50
  

  
  
  
  

add a comment | 

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 (𝟙𝟚𝟛😎😜🙃 etc), call the string iterator and check how many items it returns, which can be done with spread or Array.from (because otherwise, str.length won't evaluate to the right number of individual characters):

function isUnique(str) 
 return new Set(str).size === [...str].length;


console.log(isUnique('😜'));
console.log(isUnique('😜😜'));

share|improve this answer

edited Apr 3 at 6:03

Patrick Roberts

21.3k33777

answered Apr 3 at 5:37

CertainPerformanceCertainPerformance

101k166292

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'))

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


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

function isUnique(str) 
 return new Set(str).size === [...str].length;


console.log(isUnique('😜'));
console.log(isUnique('😜😜'));

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'))

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'))

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


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

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


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

function isUnique(str) 
 return new Set(str).size === [...str].length;


console.log(isUnique('😜'));
console.log(isUnique('😜😜'));

function isUnique(str) 
 return new Set(str).size === [...str].length;


console.log(isUnique('😜'));
console.log(isUnique('😜😜'));

share|improve this answer

edited Apr 3 at 6:03

Patrick Roberts

21.3k33777

answered Apr 3 at 5:37

CertainPerformanceCertainPerformance

101k166292

edited Apr 3 at 6:03

Patrick Roberts

21.3k33777

edited Apr 3 at 6:03

Patrick Roberts

21.3k33777

answered Apr 3 at 5:37

CertainPerformanceCertainPerformance

101k166292

answered Apr 3 at 5:37

CertainPerformanceCertainPerformance

101k166292

0

Only first iteration in your for loop is run (because you always execute 'return'). Instead you can use following code

function isUnique(str, t=) 
 
 return ![...str].some(c=> t[c]=c in t)


console.log('heloworld =>',isUnique('heloworld'));
console.log('helo =>',isUnique('helo'));

share|improve this answer

edited Apr 3 at 8:07

answered Apr 3 at 5:52

Kamil KiełczewskiKamil Kiełczewski

14.5k87497

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why is r a parameter?
  
  – JollyJoker
  Apr 3 at 8:01
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  r (I rename it to t) is temporary hash map (define in tricky way as default param)
  
  – Kamil Kiełczewski
  Apr 3 at 8:07
  
  

  
  
  
  

add a comment | 

0

Only first iteration in your for loop is run (because you always execute 'return'). Instead you can use following code

function isUnique(str, t=) 
 
 return ![...str].some(c=> t[c]=c in t)


console.log('heloworld =>',isUnique('heloworld'));
console.log('helo =>',isUnique('helo'));

share|improve this answer

edited Apr 3 at 8:07

answered Apr 3 at 5:52

Kamil KiełczewskiKamil Kiełczewski

14.5k87497

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why is r a parameter?
  
  – JollyJoker
  Apr 3 at 8:01
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  r (I rename it to t) is temporary hash map (define in tricky way as default param)
  
  – Kamil Kiełczewski
  Apr 3 at 8:07
  
  

  
  
  
  

add a comment | 

Only first iteration in your for loop is run (because you always execute 'return'). Instead you can use following code

function isUnique(str, t=) 
 
 return ![...str].some(c=> t[c]=c in t)


console.log('heloworld =>',isUnique('heloworld'));
console.log('helo =>',isUnique('helo'));

share|improve this answer

edited Apr 3 at 8:07

answered Apr 3 at 5:52

Kamil KiełczewskiKamil Kiełczewski

14.5k87497

function isUnique(str, t=) 
 
 return ![...str].some(c=> t[c]=c in t)


console.log('heloworld =>',isUnique('heloworld'));
console.log('helo =>',isUnique('helo'));

function isUnique(str, t=) 
 
 return ![...str].some(c=> t[c]=c in t)


console.log('heloworld =>',isUnique('heloworld'));
console.log('helo =>',isUnique('helo'));

function isUnique(str, t=) 
 
 return ![...str].some(c=> t[c]=c in t)


console.log('heloworld =>',isUnique('heloworld'));
console.log('helo =>',isUnique('helo'));

share|improve this answer

edited Apr 3 at 8:07

answered Apr 3 at 5:52

Kamil KiełczewskiKamil Kiełczewski

14.5k87497

answered Apr 3 at 5:52

Kamil KiełczewskiKamil Kiełczewski

14.5k87497

answered Apr 3 at 5:52

Kamil KiełczewskiKamil Kiełczewski

14.5k87497