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Check for characters in a string being unique

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7

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 2 days ago

Peter Mortensen

13.9k1987113

asked 2 days ago

user3763875user3763875

695

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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
  2 days ago
  

  
  
  
  

add a comment | 

7

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 2 days ago

Peter Mortensen

13.9k1987113

asked 2 days ago

user3763875user3763875

695

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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
  2 days ago
  

  
  
  
  

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 2 days ago

Peter Mortensen

13.9k1987113

asked 2 days ago

user3763875user3763875

695

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 2 days ago

Peter Mortensen

13.9k1987113

asked 2 days ago

user3763875user3763875

695

share|improve this question

edited 2 days ago

Peter Mortensen

13.9k1987113

asked 2 days ago

user3763875user3763875

695

edited 2 days ago

Peter Mortensen

13.9k1987113

edited 2 days ago

Peter Mortensen

13.9k1987113

asked 2 days ago

user3763875user3763875

695

asked 2 days ago

user3763875user3763875

695

2 Answers
2

active

oldest

votes

24

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 2 days ago

Patrick Roberts

21.2k33677

answered 2 days ago

CertainPerformanceCertainPerformance

97.8k165887

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Not sure if this matters but for multi-unit code points you get the wrong answer, e.g. isUnique('😀😁') === false
  
  – Patrick Roberts
  2 days ago
  
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  The fix is relatively simple though: return new Set(str).size === Array.from(str).length;
  
  – Patrick Roberts
  2 days ago
  

  
  
  
  

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 2 days ago

answered 2 days ago

Kamil KiełczewskiKamil Kiełczewski

14k87397

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why is r a parameter?
  
  – JollyJoker
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  r (I rename it to t) is temporary hash map (define in tricky way as default param)
  
  – Kamil Kiełczewski
  2 days ago
  
  

  
  
  
  

add a comment | 

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24

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 2 days ago

Patrick Roberts

21.2k33677

answered 2 days ago

CertainPerformanceCertainPerformance

97.8k165887

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Not sure if this matters but for multi-unit code points you get the wrong answer, e.g. isUnique('😀😁') === false
  
  – Patrick Roberts
  2 days ago
  
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  The fix is relatively simple though: return new Set(str).size === Array.from(str).length;
  
  – Patrick Roberts
  2 days ago
  

  
  
  
  

add a comment | 

24

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 2 days ago

Patrick Roberts

21.2k33677

answered 2 days ago

CertainPerformanceCertainPerformance

97.8k165887

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Not sure if this matters but for multi-unit code points you get the wrong answer, e.g. isUnique('😀😁') === false
  
  – Patrick Roberts
  2 days ago
  
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  The fix is relatively simple though: return new Set(str).size === Array.from(str).length;
  
  – Patrick Roberts
  2 days ago
  

  
  
  
  

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 2 days ago

Patrick Roberts

21.2k33677

answered 2 days ago

CertainPerformanceCertainPerformance

97.8k165887

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 2 days ago

Patrick Roberts

21.2k33677

answered 2 days ago

CertainPerformanceCertainPerformance

97.8k165887

edited 2 days ago

Patrick Roberts

21.2k33677

edited 2 days ago

Patrick Roberts

21.2k33677

answered 2 days ago

CertainPerformanceCertainPerformance

97.8k165887

answered 2 days ago

CertainPerformanceCertainPerformance

97.8k165887

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 2 days ago

answered 2 days ago

Kamil KiełczewskiKamil Kiełczewski

14k87397

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why is r a parameter?
  
  – JollyJoker
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  r (I rename it to t) is temporary hash map (define in tricky way as default param)
  
  – Kamil Kiełczewski
  2 days ago
  
  

  
  
  
  

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 2 days ago

answered 2 days ago

Kamil KiełczewskiKamil Kiełczewski

14k87397

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why is r a parameter?
  
  – JollyJoker
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  r (I rename it to t) is temporary hash map (define in tricky way as default param)
  
  – Kamil Kiełczewski
  2 days ago
  
  

  
  
  
  

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 2 days ago

answered 2 days ago

Kamil KiełczewskiKamil Kiełczewski

14k87397

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 2 days ago

answered 2 days ago

Kamil KiełczewskiKamil Kiełczewski

14k87397

answered 2 days ago

Kamil KiełczewskiKamil Kiełczewski

14k87397

answered 2 days ago

Kamil KiełczewskiKamil Kiełczewski

14k87397