Check if string has duplicate letters

An algorithm to check if there are duplicate letters in the string.

We will check if the given string has duplicate letters and if found we will return true, false otherwise.

Example

Input:
'learnersbucket'
'abcdefghijk'
'I Love learnersbucket'

Output:
true
false
true

Implementation

• We will create a Set and add letters of the string to it.
• While storing the letter we will check if Set has duplicate letters. If it is present then return true else return false.
• We will check for both case-sensitive and incase-sensitive letters.
• Everything will be written in ES6.

For incase-sensitive letters

let containsDuplicates = (str) => {
  let set = new Set();
  
  //convert str to lowercase
  //Remove this if you want to check for incase-sensitive strings
  str = str.toLowerCase();
  
  //If it is not whitespace the check if aplhabet is present or not
  for(let i = 0; i < str.length; i++){

   if(str[i] != ' '){

    if(set.has(str[i])){
      return true;
    }

     set.add(str[i]);
    }
  }
  
  return false;
}

Input:
console.log(containsDuplicates("learnersbucket"));
console.log(containsDuplicates("abcdefghijk"));
console.log(containsDuplicates("I Love learnersbucket"));

Output:
true
false
true

---

For case-sensitive letters

let containsDuplicates = (str) => {
  let set = new Set();
  
  //If it is not whitespace the check if aplhabet is present or not
  for(let i = 0; i < str.length; i++){

   if(str[i] != ' '){

    if(set.has(str[i])){
      return true;
    }

     set.add(str[i]);
    }
  }
  
  return false;
}

Input:
console.log(containsDuplicates("learnersbucket"));
console.log(containsDuplicates("abcdefghijk"));
console.log(containsDuplicates("I Luv life"));

Output:
true
false
false

Time Complexity: O(n).
Space Complexity: O(n).

Time and Space complexity

• We are traversing whole string and will be checking each character of it, so Time complexity is O(n).
• We will be storing each character of given string, so Space complexity is O(n).