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Check if a string is Isogram or not

Last Updated : 19 Sep, 2022
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Given a word or phrase, check if it is an isogram or not. An Isogram is a word in which no letter occurs more than once

Examples: 

Input: Machine
Output: True
Explanation: "Machine" does not have any character repeating, it is an Isogram

Input : Geek
Output : False
Explanation: "Geek" has 'e' as repeating character, it is not an Isogram

Check if a string is Isogram or not using sorting:

To solve the problem follow the below idea:

Sort the string and for every character check, if the current character is equal to the previous character or not. If it is equal then the string is not an isogram

Follow the given steps to solve the problem:

  • Convert the string into lowercase English letters
  • Sort the string
  • Traverse the string and check for every character
    • If the current character is equal to the character on the previous index then return false
  • Return true

Below is the implementation of the above approach:

C++ 
// C++ program to check // If a given string is isogram or not #include <bits/stdc++.h> using namespace std; // Function to check // If a given string is isogram or not string is_isogram(string str) {  int len = str.length();  // Convert the string in lower case letters  for (int i = 0; i < len; i++)  str[i] = tolower(str[i]);  sort(str.begin(), str.end());  for (int i = 0; i < len; i++) {  if (str[i] == str[i + 1])  return "False";  }  return "True"; } // Driver code int main() {  string str1 = "Machine";    // Function call  cout << is_isogram(str1) << endl;  string str2 = "isogram";    // Function call  cout << is_isogram(str2) << endl;  string str3 = "GeeksforGeeks";    // Function call  cout << is_isogram(str3) << endl;  string str4 = "Alphabet";    // Function call  cout << is_isogram(str4) << endl;  return 0; } // Contributed by nuclode
Java 
// Java program to check // if a given string is isogram or not import java.io.*; import java.util.*; class GFG {  // Function to check  // if a given string is isogram or not  static boolean is_isogram(String str)  {  // Convert the string in lower case letters  str = str.toLowerCase();  int len = str.length();  char arr[] = str.toCharArray();  Arrays.sort(arr);  for (int i = 0; i < len - 1; i++) {  if (arr[i] == arr[i + 1])  return false;  }  return true;  }  // Driver code  public static void main(String[] args)  {  String str1 = "Machine";    // Function call  System.out.println(is_isogram(str1));  String str2 = "isogram";    // Function call  System.out.println(is_isogram(str2));  String str3 = "GeeksforGeeks";    // Function call  System.out.println(is_isogram(str3));  String str4 = "Alphabet";    // Function call  System.out.println(is_isogram(str4));  } } // Contributed by Pramod Kumar
Python3 
# Python program to check # if a word is isogram or not def is_isogram(word): # Convert the word or sentence in lower case letters. clean_word = word.lower() # Make an empty list to append unique letters letter_list = [] for letter in clean_word: # If letter is an alphabet then only check if letter.isalpha(): if letter in letter_list: return False letter_list.append(letter) return True # Driver code if __name__ == '__main__': # Function call print(is_isogram("Machine")) print(is_isogram("isogram")) print(is_isogram("GeeksforGeeks")) print(is_isogram("Alphabet "))
C# 
// C# program to check if a given // string is isogram or not using System; public class GFG {    // Function to check if a given  // string is isogram or not  static bool is_isogram(string str)  {  // Convert the string in lower case letters  str = str.ToLower();  int len = str.Length;  char[] arr = str.ToCharArray();  Array.Sort(arr);  for (int i = 0; i < len - 1; i++) {  if (arr[i] == arr[i + 1])  return false;  }  return true;  }  // Driver code  public static void Main()  {  string str1 = "Machine";    // Function call  Console.WriteLine(is_isogram(str1));  string str2 = "isogram";    // Function call  Console.WriteLine(is_isogram(str2));  string str3 = "GeeksforGeeks";    // Function call  Console.WriteLine(is_isogram(str3));  string str4 = "Alphabet";    // Function call  Console.WriteLine(is_isogram(str4));  } } // This code is contributed by Sam007
JavaScript 
<script>  // Javascript program to check if a given  // string is isogram or not    // Function to check if a given  // string is isogram or not  function is_isogram(str)  {  // Convert the string in lower case letters  str = str.toLowerCase();  let len = str.length;    let arr = str.split('');    arr.sort();  for (let i = 0; i < len - 1; i++) {  if (arr[i] == arr[i + 1])  return false;  }  return true;  }    let str1 = "Machine";  if(is_isogram(str1))  {  document.write("True" + "</br>");  }  else{  document.write("False" + "</br>");  }  let str2 = "isogram";  if(is_isogram(str2))  {  document.write("True" + "</br>");  }  else{  document.write("False" + "</br>");  }  let str3 = "GeeksforGeeks";  if(is_isogram(str3))  {  document.write("True" + "</br>");  }  else{  document.write("False" + "</br>");  }  let str4 = "Alphabet";  if(is_isogram(str4))  {  document.write("True" + "</br>");  }  else{  document.write("False" + "</br>");  }    // This code is contributed by suresh07. </script>

Output
True True False False

Time Complexity: O(N log N)
Auxiliary Space: O(1)

Check if a string is Isogram or not using Hash-Map:

To solve the problem follow the below idea:

In this, the count of characters of the string is stored in the hashmap, and wherever it is found to be greater than 1 for any char, return false else return true at the end

Follow the given steps to solve the problem:

  • Declare a hashmap to store the count of the characters of the string
  • Traverse the string
    • Increase the count of the current character in the hashmap
    • If the count of the current character is greater than one then return false
  • Return true

Below is the implementation of the above approach:

C++ 
// CPP code to check string is isogram or not #include <bits/stdc++.h> using namespace std; // function to check isogram bool check_isogram(string str) {  int length = str.length();  int mapHash[26] = { 0 };  // loop to store count of chars and check if it is  // greater than 1  for (int i = 0; i < length; i++) {  mapHash[str[i] - 'a']++;  // if count > 1, return false  if (mapHash[str[i] - 'a'] > 1) {  return false;  }  }  return true; } // Driver code int main() {  string str = "geeks";  string str2 = "computer";  // checking str as isogram  if (check_isogram(str)) {  cout << "True" << endl;  }  else {  cout << "False" << endl;  }  // checking str2 as isogram  if (check_isogram(str2)) {  cout << "True" << endl;  }  else {  cout << "False" << endl;  }  return 0; }
Java 
// Java code to check string is isogram or not import java.io.*; class GFG {  // function to check isogram  static boolean check_isogram(String str)  {  int length = str.length();  int mapHash[] = new int[26];  // loop to store count of chars and  // check if it is greater than 1  for (int i = 0; i < length; i++) {  mapHash[str.charAt(i) - 'a']++;  // if count > 1, return false  if (mapHash[str.charAt(i) - 'a'] > 1) {  return false;  }  }  return true;  }  // Driver code  public static void main(String[] args)  {  String str = "geeks";  String str2 = "computer";  // checking str as isogram  if (check_isogram(str))  System.out.println("True");  else  System.out.println("False");  // checking str2 as isogram  if (check_isogram(str2))  System.out.println("True");  else  System.out.println("False");  } } // This code contributed by Rajput-Ji
Python3 
# Python3 code to check string is isogram or not # function to check isogram def check_isogram(string): length = len(string) mapHash = [0] * 26 # loop to store count of chars # and check if it is greater than 1 for i in range(length): mapHash[ord(string[i]) - ord('a')] += 1 # if count > 1, return false if (mapHash[ord(string[i]) - ord('a')] > 1): return False return True # Driver code if __name__ == "__main__": string = "geeks" string2 = "computer" # checking str as isogram if (check_isogram(string)): print("True") else: print("False") # checking str2 as isogram if (check_isogram(string2)): print("True") else: print("False") # This code is contributed by AnkitRai01
C# 
// C# code to check string is isogram or not using System; public class GFG {  // function to check isogram  static bool check_isogram(String str)  {  int length = str.Length;  int[] mapHash = new int[26];  // loop to store count of chars and  // check if it is greater than 1  for (int i = 0; i < length; i++) {  mapHash[str[i] - 'a']++;  // if count > 1, return false  if (mapHash[str[i] - 'a'] > 1) {  return false;  }  }  return true;  }  // Driver code  public static void Main(String[] args)  {  String str = "geeks";  String str2 = "computer";  // checking str as isogram  if (check_isogram(str))  Console.WriteLine("True");  else  Console.WriteLine("False");  // checking str2 as isogram  if (check_isogram(str2))  Console.WriteLine("True");  else  Console.WriteLine("False");  } } // This code has been contributed by 29AjayKumar
JavaScript 
<script>  // Javascript code to check string is isogram or not     // function to check isogram   function check_isogram(str)   {   let length = str.length;   let mapHash = new Array(26);  mapHash.fill(0);  // loop to store count of chars and   // check if it is greater than 1   for (let i = 0; i < length; i++)   {   mapHash[str[i].charCodeAt() - 'a'.charCodeAt()]++;   // if count > 1, return false   if (mapHash[str[i].charCodeAt() - 'a'.charCodeAt()] > 1)   {   return false;   }   }   return true;   }     let str = "geeks";   let str2 = "computer";     // checking str as isogram   if (check_isogram(str))   document.write("True" + "</br>");  else  document.write("False" + "</br>");    // checking str2 as isogram   if (check_isogram(str2))   document.write("True" + "</br>");  else  document.write("False" + "</br>");    // This code is contributed by divyeshrabadiya07. </script>

Output
False True

Time Complexity: O(N)
Auxiliary Space: O(1), as an array of fixed size 26 is used.

Thanks Sahil Bansal for suggesting the above method. 
If you like GeeksforGeeks (We know you do!) and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org.


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Sakshi_Tiwari
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