Efficiently check if a string has all unique characters without using any additional data structure - GeeksforGeeks

20 Apr, 2022
Implement an space efficient algorithm to determine if a string (of characters from ‘a’ to ‘z’) has all unique characters or not. Use additional data structures like count array, hash, etc is not allowed.Expected Time Complexity : O(n) Examples :  
Input  : str = "aaabbccdaa"
Output : No

Input  : str = "abcd"
Output : Yes
 
The idea is to use an integer variable and use bits in its binary representation to store whether a character is present or not. Typically an integer has at-least 32 bits and we need to store presence/absence of only 26 characters.Below is the implementation of the idea. 
C++
Java
Python3
C#
PHP
Javascript
// A space efficient C++ program to check if// all characters of string are unique.#include<bits/stdc++.h>using namespace std; // Returns true if all characters of str are// unique.// Assumptions : (1) str contains only characters//                   from 'a' to 'z'//               (2) integers are stored using 32//                   bitsbool areChractersUnique(string str){    // An integer to store presence/absence    // of 26 characters using its 32 bits.    int checker = 0;     for (int i = 0; i < str.length(); ++i)    {        int val = (str[i]-'a');         // If bit corresponding to current        // character is already set        if ((checker & (1 << val)) > 0)            return false;         // set bit in checker        checker |=  (1 << val);    }     return true;} // Driver codeint main(){    string s = "aaabbccdaa";    if (areChractersUnique(s))        cout << "Yes";    else        cout << "No";    return 0;}
// A space efficient Java program to check if// all characters of string are unique.class GFG {             // Returns true if all characters of str are    // unique.    // Assumptions : (1) str contains only characters    //                 from 'a' to 'z'    //             (2) integers are stored using 32    //                 bits    static boolean areChractersUnique(String str)    {                 // An integer to store presence/absence        // of 26 characters using its 32 bits.        int checker = 0;             for (int i = 0; i < str.length(); ++i)        {            int val = (str.charAt(i)-'a');                 // If bit corresponding to current            // character is already set            if ((checker & (1 << val)) > 0)                return false;                 // set bit in checker            checker |= (1 << val);        }             return true;    }         //driver code    public static void main (String[] args)    {        String s = "aaabbccdaa";                 if (areChractersUnique(s))            System.out.print("Yes");        else            System.out.print("No");    }} // This code is contributed by Anant Agarwal.
# A space efficient Python3 program to check if# all characters of string are unique # Returns true if all characters of str are# unique.# Assumptions : (1) str contains only characters#                    from 'a' to 'z'#                (2) integers are stored using 32#                    bits def areCharactersUnique(s):         # An integer to store presence/absence    # of 26 characters using its 32 bits    checker = 0         for i in range(len(s)):                 val = ord(s[i]) - ord('a')                 # If bit corresponding to current        # character is already set        if (checker & (1 << val)) > 0:            return False                 # set bit in checker        checker |= (1 << val)             return True     # Driver codes = "aaabbccdaa"if areCharactersUnique(s):    print("Yes")else:    print("No")     # This code is contributed# by Mohit Kumar
// A space efficient program// to check if all characters// of string are unique.using System; class GFG {     // Returns true if all characters    // of str are unique. Assumptions:    // (1)str contains only characters    // from 'a' to 'z'.(2)integers are    // stored using 32 bits    static bool areChractersUnique(string str)    {        // An integer to store presence        // or absence of 26 characters        // using its 32 bits.        int checker = 0;         for (int i = 0; i < str.Length; ++i) {            int val = (str[i] - 'a');             // If bit corresponding to current            // character is already set            if ((checker & (1 << val)) > 0)                return false;             // set bit in checker            checker |= (1 << val);        }         return true;    }     // Driver code    public static void Main()    {        string s = "aaabbccdaa";         if (areChractersUnique(s))            Console.Write("Yes");        else            Console.Write("No");    }} // This code is contributed by Anant Agarwal.
<?php// A space efficient PHP program// to check if all characters of// string are unique. // Returns true if all characters// of str are unique.// Assumptions : (1) str contains//                     only characters//                   from 'a' to 'z'//         (2) integers are stored//             using 32 bitsfunction areChractersUnique($str){    // An integer to store presence/absence    // of 26 characters using its 32 bits.    $checker = 0;     for ($i = 0; $i < $len = strlen($str); ++$i)    {        $val = ($str[$i] - 'a');         // If bit corresponding to current        // character is already set        if (($checker & (1 << $val)) > 0)            return false;         // set bit in checker        $checker |= (1 << $val);    }     return true;} // Driver code$s = "aaabbccdaa";if (areChractersUnique($s))    echo "Yes";else    echo "No"; // This code is contributed by aj_36?>
<script> // Javascript program for the above approach      // Returns true if all characters of str are    // unique.    // Assumptions : (1) str contains only characters    //                   from 'a' to 'z'    //               (2) integers are stored using 32    //                 bits    function areChractersUnique(str)    {                 // An integer to store presence/absence        // of 26 characters using its 32 bits.        let checker = 0;             for (let i = 0; i < str.length; ++i)        {            let val = (str[i]-'a');                 // If bit corresponding to current            // character is already set            if ((checker & (1 << val)) > 0)                return false;                 // set bit in checker            checker |= (1 << val);        }             return true;    } // Driver Code         var s = "aaabbccdaa";             if (areChractersUnique(s))        document.write("Yes");    else        document.write("No"); </script>
No
Time Complexity : O(n) Auxiliary Space : O(1)
Another Implementation: Using STL
C++
Java
Python3
C#
Javascript
#include <bits/stdc++.h>using namespace std;bool unique(string s) {    sort(s.begin(),s.end());    for(int i=0;i<s.size()-1;i++)    {        if(s[i]==s[i+1])        {            return false;            break;        }    }    return true;}int main() {  if(unique("abcdd")==true)  {         cout <<"String is Unique"<<endl;  }  else  {    cout <<"String is not Unique"<<endl;  }      return 0;}
import java.util.Arrays; class GFG {     static boolean unique(String s)    {        Arrays.sort(s.toCharArray());        for (int i = 0; i < s.length()-1; i++) {            if (s.charAt(i) == s.charAt(i + 1)) {                return false;            }        }        return true;    }     public static void main(String[] args)    {        if (unique("abcdd") == true) {            System.out.println("String is Unique");        }        else {            System.out.println("String is not Unique");        }    }} // This code is contributed by rajsanghavi9.
def unique(s):    s = list(s)    s.sort()    for i in range (len(s) - 1):             if(s[i] == s[i + 1]):                     return False            break          return True if(unique("abcdd") == True):  print("String is Unique")     else:  print("String is not Unique") # This code is contributed by shivanisinghss2110
using System; public class GFG {     static bool unique(String s) {        Array.Sort(s.ToCharArray());        for (int i = 0; i < s.Length-1; i++) {            if (s[i] == s[i + 1]) {                return false;            }        }        return true;    }   // Driver code    public static void Main(String[] args) {        if (unique("abcdd") == true) {            Console.WriteLine("String is Unique");        } else {            Console.WriteLine("String is not Unique");        }    }} // This code is contributed by umadevi9616
<script>    function unique(s) {                 for (var i = 0; i < s.length-1; i++) {            if (s.charAt(i) == s.charAt(i + 1)) {                return false;            }        }        return true;    }              if (unique("abcdd") == true) {            document.write("String is Unique");        } else {            document.write("String is not Unique");        } // This code is contributed by umadevi9616.</script>
String is not Unique
This article is contributed by Mr. Somesh Awasthi. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. 
jit_t
mohit kumar 29
RShriwas
code_hunt
siddharth_25
rajsanghavi9
umadevi9616
shivanisinghss2110
simmytarika5
mayur thorat
surinderdawra388
Bit Magic
Strings
Strings
Bit Magic
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.
Cyclic Redundancy Check and Modulo-2 Division
Little and Big Endian Mystery
Binary representation of a given number
Add two numbers without using arithmetic operators
Bit Fields in C
Reverse a string in Java
Write a program to reverse an array or string
Longest Common Subsequence | DP-4
Write a program to print all permutations of a given string
C++ Data Types