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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