Efficiently find first repeated character in a string without using any additional data structure in one traversal
Implement a space efficient algorithm to check First repeated character in a string without using any additional data structure in one traversal. Use additional data structures like count array, hash, etc is not allowed.
Examples :
Input : abcfdeacf Output : char = a, index= 6
The idea is to use an integer variable and uses 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.
C++
// Efficiently check First repeated character// in C++ program#include<bits/stdc++.h>using namespace std;// Returns -1 if all characters of str are// unique.// Assumptions : (1) str contains only characters// from 'a' to 'z'// (2) integers are stored using 32// bitsint FirstRepeated(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 i; // set bit in checker checker |= (1 << val); } return -1;}// Driver codeint main(){ string s = "abcfdeacf"; int i=FirstRepeated(s); if (i!=-1) cout <<"Char = "<< s[i] << " and Index = "<<i; else cout << "No repeated Char"; return 0;} |
Java
// Efficiently check First repeated character// in Java programpublic class First_Repeated_char { static int FirstRepeated(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 i; // set bit in checker checker |= (1 << val); } return -1; } // Driver code public static void main(String args[]) { String s = "abcfdeacf"; int i=FirstRepeated(s); if (i!=-1) System.out.println("Char = "+ s.charAt(i) + " and Index = "+i); else System.out.println( "No repeated Char"); }}// This code is contributed by Sumit Ghosh |
Python
# Efficiently check First repeated character# in Python# Returns -1 if all characters of str are# unique.# Assumptions : (1) str contains only characters# from 'a' to 'z'## (2) integers are stored using 32## bitsdef FirstRepeated(string): # An integer to store presence/absence # of 26 characters using its 32 bits. checker = 0 pos = 0 for i in string: val = ord(i) - ord('a'); # If bit corresponding to current # character is already set if ((checker & (1 << val)) > 0): return pos # set bit in checker checker |= (1 << val) pos += 1 return -1 # Driver codestring = "abcfdeacf"i = FirstRepeated(string)if i != -1: print "Char = ", string[i], " and Index = ", i;else: print "No repeated Char"# This code is contributed by Sachin Bisht |
C#
// C# program to Efficiently// check First repeated characterusing System;public class First_Repeated_char { static int FirstRepeated(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 i; // set bit in checker checker |= (1 << val); } return -1; } // Driver code public static void Main() { string s = "abcfdeacf"; int i=FirstRepeated(s); if (i!=-1) Console.WriteLine("Char = " + s[i] + " and Index = " + i); else Console.WriteLine( "No repeated Char"); }}// This code is contributed by vt_m. |
PHP
<?php// Efficiently check First repeated character// in PHP program// Returns -1 if all characters of str are// unique.// Assumptions : (1) str contains only characters// from 'a' to 'z'// (2) integers are stored using 32// bitsfunction FirstRepeated($str){ // An integer to store presence/absence // of 26 characters using its 32 bits. $checker = 0; for ($i = 0; $i < strlen($str); ++$i) { $val = (ord($str[$i]) - ord('a')); // If bit corresponding to current // character is already set if (($checker & (1 << $val)) > 0) return $i; // set bit in checker $checker |= (1 << $val); } return -1;}// Driver code$s = "abcfdeacf";$i=FirstRepeated($s);if ($i!=-1) echo "Char = " . $s[$i] . " and Index = " . $i;else echo "No repeated Char";// This code is contributed by ita_c?> |
Javascript
<script>// Efficiently check First repeated character// in Javascript program function FirstRepeated(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 i; // set bit in checker checker |= (1 << val); } return -1; } // Driver code let s = "abcfdeacf"; let i=FirstRepeated(s); if (i!=-1) document.write("Char = "+ s[i] + " and Index = "+i); else document.write( "No repeated Char"); // This code is contributed by rag2127 </script> |
Output:
Char = a and Index = 6
Time Complexity: O(n)
Auxiliary Space: O(1)
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