Repeated Character Whose First Appearance is Leftmost
Given a string, find the repeated character present first in the string.
Examples:
Input : geeksforgeeks Output : g (mind that it will be g, not e.) Input : abcdabcd Output : a Input : abcd Output : -1 No character repeats
Asked in: Goldman Sachs internship
We have discussed different approaches in Find repeated character present first in a string.
How to solve this problem using one traversal of input string?
Method 1 (Traversing from Left to Right) We traverse the string from left to right. We keep track of the leftmost index of every character. If a character repeats, we compare its leftmsot index with current result and update the result if result is greater
C++
// CPP program to find first repeating // character #include <bits/stdc++.h> using namespace std; #define NO_OF_CHARS 256 /* The function returns index of the first repeating character in a string. If all characters are repeating then returns -1 */int firstRepeating(string& str) { // Initialize leftmost index of every // character as -1. int firstIndex[NO_OF_CHARS]; for (int i = 0; i < NO_OF_CHARS; i++) firstIndex[i] = -1; // Traverse from left and update result // if we see a repeating character whose // first index is smaller than current // result. int res = INT_MAX; for (int i = 0; i < str.length(); i++) { if (firstIndex[str[i]] == -1) firstIndex[str[i]] = i; else res = min(res, firstIndex[str[i]]); } return (res == INT_MAX) ? -1 : res; } /* Driver program to test above function */int main() { string str = "geeksforgeeks"; int index = firstRepeating(str); if (index == -1) printf("Either all characters are " "distinct or string is empty"); else printf("First Repeating character" " is %c", str[index]); return 0; } |
chevron_right
filter_none
Java
// Java program to find first repeating // character class GFG { static int NO_OF_CHARS = 256; /* The function returns index of the first repeating character in a string. If all characters are repeating then returns -1 */ static int firstRepeating(char[] str) { // Initialize leftmost index of every // character as -1. int[] firstIndex = new int[NO_OF_CHARS]; for (int i = 0; i < NO_OF_CHARS; i++) { firstIndex[i] = -1; } // Traverse from left and update result // if we see a repeating character whose // first index is smaller than current // result. int res = Integer.MAX_VALUE; for (int i = 0; i < str.length; i++) { if (firstIndex[str[i]] == -1) { firstIndex[str[i]] = i; } else { res = Math.min(res, firstIndex[str[i]]); } } return (res == Integer.MAX_VALUE) ? -1 : res; } /* Driver code */ public static void main(String[] args) { char[] str = "geeksforgeeks".toCharArray(); int index = firstRepeating(str); if (index == -1) { System.out.printf("Either all characters are " + "distinct or string is empty"); } else { System.out.printf("First Repeating character" + " is %c", str[index]); } } } // This code has been contributed by 29AjayKumar |
chevron_right
filter_none
Python3
# Python 3 program to find first repeating # character import sys NO_OF_CHARS = 256 # The function returns index of the first # repeating character in a string. If # all characters are repeating then # returns -1 */ def firstRepeating(str): # Initialize leftmost index of every # character as -1. firstIndex = [0 for i in range(NO_OF_CHARS)] for i in range(NO_OF_CHARS): firstIndex[i] = -1 # Traverse from left and update result # if we see a repeating character whose # first index is smaller than current # result. res = sys.maxsize for i in range(len(str)): if (firstIndex[ord(str[i])] == -1): firstIndex[ord(str[i])] = i else: res = min(res, firstIndex[ord(str[i])]) if res == sys.maxsize: return -1 else: return res # Driver function if __name__ == '__main__': str = "geeksforgeeks" index = firstRepeating(str) if (index == -1): print("Either all characters are distinct or string is empty") else: print("First Repeating character is",str[index]) # This code is contributed by # Surendra_Gangwar |
chevron_right
filter_none
C#
// C# program to find first repeating // character using System; using System.Collections.Generic; class GFG { static int NO_OF_CHARS = 256; /* The function returns index of the first repeating character in a string. If all characters are repeating then returns -1 */ static int firstRepeating(char[] str) { // Initialize leftmost index of every // character as -1. int[] firstIndex = new int[NO_OF_CHARS]; for (int i = 0; i < NO_OF_CHARS; i++) { firstIndex[i] = -1; } // Traverse from left and update result // if we see a repeating character whose // first index is smaller than current // result. int res = int.MaxValue; for (int i = 0; i < str.Length; i++) { if (firstIndex[str[i]] == -1) { firstIndex[str[i]] = i; } else { res = Math.Min(res, firstIndex[str[i]]); } } return (res == int.MaxValue) ? -1 : res; } /* Driver code */ public static void Main(String[] args) { char[] str = "geeksforgeeks".ToCharArray(); int index = firstRepeating(str); if (index == -1) { Console.Write("Either all characters are " + "distinct or string is empty"); } else { Console.Write("First Repeating character" + " is {0}", str[index]); } } } // This code is contributed by Princi Singh |
chevron_right
filter_none
Output:
First Repeating character is g
Time Complexity : O(n). It does only one traversal of input string.
Auxiliary Space : O(1)
Method 2 (Traversing Right to Left) We traverse the string from right to left. We keep track of the visited characters. If a character repeats, we update the result.
C++
// CPP program to find first repeating // character #include <bits/stdc++.h> using namespace std; #define NO_OF_CHARS 256 /* The function returns index of the first repeating character in a string. If all characters are repeating then returns -1 */int firstRepeating(string& str) { // Mark all characters as not visited bool visited[NO_OF_CHARS]; for (int i = 0; i < NO_OF_CHARS; i++) visited[i] = false; // Traverse from right and update res as soon // as we see a visited character. int res = -1; for (int i = str.length() - 1; i >= 0; i--) { if (visited[str[i]] == false) visited[str[i]] = true; else res = i; } return res; } /* Driver program to test above function */int main() { string str = "geeksforgeeks"; int index = firstRepeating(str); if (index == -1) printf("Either all characters are " "distinct or string is empty"); else printf("First Repeating character" " is %c", str[index]); return 0; } |
chevron_right
filter_none
Java
// Java program to find first repeating // character import java.util.*; class GFG { static int NO_OF_CHARS= 256; /* The function returns index of the first repeating character in a string. If all characters are repeating then returns -1 */static int firstRepeating(String str) { // Mark all characters as not visited boolean []visited = new boolean[NO_OF_CHARS]; for (int i = 0; i < NO_OF_CHARS; i++) visited[i] = false; // Traverse from right and update res as soon // as we see a visited character. int res = -1; for (int i = str.length() - 1; i >= 0; i--) { if (visited[str.charAt(i)] == false) visited[str.charAt(i)] = true; else res = i; } return res; } /* Driver code */public static void main(String[] args) { String str = "geeksforgeeks"; int index = firstRepeating(str); if (index == -1) System.out.printf("Either all characters are " +"distinct or string is empty"); else System.out.printf("First Repeating character" +" is %c", str.charAt(index)); } } // This code contributed by Rajput-Ji |
chevron_right
filter_none
Python3
# Python3 program to find first # repeating character NO_OF_CHARS = 256 """ The function returns index of the first repeating character in a string. If all characters are repeating then returns -1 """ def firstRepeating(string) : # Mark all characters as not visited visited = [False] * NO_OF_CHARS; for i in range(NO_OF_CHARS) : visited[i] = False; # Traverse from right and update res as soon # as we see a visited character. res = -1; for i in range(len(string)-1, -1 , -1) : if (visited[string.index(string[i])] == False): visited[string.index(string[i])] = True; else: res = i; return res; # Driver program to test above function if __name__ == "__main__" : string = "geeksforgeeks"; index = firstRepeating(string); if (index == -1) : print("Either all characters are" , "distinct or string is empty"); else : print("First Repeating character is:", string[index]); # This code is contributed by AnkitRai01 |
chevron_right
filter_none
C#
// C# program to find first repeating // character using System; class GFG { static int NO_OF_CHARS = 256; /* The function returns index of the first repeating character in a string. If all characters are repeating then returns -1 */static int firstRepeating(String str) { // Mark all characters as not visited Boolean []visited = new Boolean[NO_OF_CHARS]; for (int i = 0; i < NO_OF_CHARS; i++) visited[i] = false; // Traverse from right and update res as soon // as we see a visited character. int res = -1; for (int i = str.Length - 1; i >= 0; i--) { if (visited[str[i]] == false) visited[str[i]] = true; else res = i; } return res; } // Driver Code public static void Main(String[] args) { String str = "geeksforgeeks"; int index = firstRepeating(str); if (index == -1) Console.Write("Either all characters are " + "distinct or string is empty"); else Console.Write("First Repeating character" + " is {0}", str[index]); } } // This code is contributed by PrinciRaj1992 |
chevron_right
filter_none
Output:
First Repeating character is g
Time Complexity : O(n). It does only one traversal of input string.
Auxiliary Space : O(1)
The method 2 is better than method 1 as it does fewer comparisons.
Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.
