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++
// 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 // bits bool 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 code int main() { string s = "aaabbccdaa" ; if (areChractersUnique(s)) cout << "Yes" ; else cout << "No" ; return 0; } |
Java
// 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. |
Python3
# A space efficeint c++ 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 code s = "aaabbccdaa" if areCharactersUnique(s): print ( "Yes" ) else : print ( "No" ) # This code is contributed # by Mohit Kumar |
.
C#
// 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
<?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 bits function 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 ?> |
Output :
No
Time Complexity : O(n)
Auxiliary Space : O(1)
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