Repeated Character Whose First Appearance is Leftmost
Last Updated :
11 Jul, 2025
Given a string, find the repeated character present first in the string.
Examples:
Input: geeksforgeeks
Output: g
Input: abcdabcd
Output: a
Input: abcd
Output: -1
Brute Force Approach:
The brute force approach to solve this problem is to consider each character in the string and then check whether it appears again in the remaining part of the string. If it does, then we have found the first repeating character.
Steps that were to follow the above approach:
- Start by iterating through each character in the string.
- For each character, iterate through the remaining characters in the string to check if there is a repeating character.
- If a repeating character is found, return the index of the first occurrence of that character.
- If no repeating character is found, return -1 to indicate that all characters in the string are distinct.
Below is the code to implement the above steps:
C++
// CPP program to find first repeating
// character
#include <bits/stdc++.h>
using namespace std;
/* The function returns index of the first
repeating character in a string. If
all characters are repeating then
returns -1 */
int firstRepeating(string& str)
{
int n = str.length();
// Consider each character
for (int i = 0; i < n; i++) {
// Check if this character appears again
for (int j = i + 1; j < n; j++) {
if (str[i] == str[j]) {
return i;
}
}
}
// If no repeating character found
return -1;
}
/* 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;
}
// Java program implementation to find first repeating
// character
import java.util.*;
public class Main {
// The function returns index of the first
// repeating character in a string. If all
// characters are repeating then returns -1
public static int firstRepeating(String str) {
int n = str.length();
// Consider each character
for (int i = 0; i < n; i++) {
// Check if this character appears again
for (int j = i + 1; j < n; j++) {
if (str.charAt(i) == str.charAt(j)) {
return i;
}
}
}
// If no repeating character found
return -1;
}
// Driver code
public static void main(String[] args) {
String str = "geeksforgeeks";
int index = firstRepeating(str);
if (index == -1)
System.out.println("Either all characters are distinct or string is empty");
else
System.out.println("First Repeating character is " + str.charAt(index));
}
}
def first_repeating(str):
n = len(str)
# Consider each character
for i in range(n):
# Check if this character appears again
for j in range(i + 1, n):
if str[i] == str[j]:
return i
# If no repeating character found
return -1
# Driver program to test above function
str = "geeksforgeeks"
index = first_repeating(str)
if index == -1:
print("Either all characters are distinct or string is empty")
else:
print(f"First Repeating character is {str[index]}")
using System;
class Program
{
/* 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)
{
int n = str.Length;
// Consider each character
for (int i = 0; i < n; i++)
{
// Check if this character appears again
for (int j = i + 1; j < n; j++)
{
if (str[i] == str[j])
{
return i;
}
}
}
// If no repeating character found
return -1;
}
/* Driver program to test above function */
static void Main(string[] args)
{
string str = "geeksforgeeks";
int index = FirstRepeating(str);
if (index == -1)
{
Console.WriteLine("Either all characters are distinct or string is empty");
}
else
{
Console.WriteLine("First Repeating character is " + str[index]);
}
}
}
function firstRepeating(str) {
let n = str.length;
// Consider each character
for (let i = 0; i < n; i++) {
// Check if this character appears again
for (let j = i + 1; j < n; j++) {
if (str[i] === str[j]) {
return i;
}
}
}
// If no repeating character found
return -1;
}
// Driver program to test above function
let str = "geeksforgeeks";
let index = firstRepeating(str);
if (index === -1)
console.log("Either all characters are distinct or string is empty");
else
console.log("First Repeating character is " + str[index]);
OutputFirst Repeating character is g
Time Complexity: O(N^2)
Auxiliary Space: O(1)
Repeated Character Whose First Appearance is Leftmost by Tracking First Occurrence:
The idea is to keep track of first occurrence of every character and whenever a character repeats check whether it is first repeated character or not.
Follow the steps to solve the problem:
- Initialise an array firstIndex of size 256 which keeps track of the first occurrence of every character in the string.
- Traverse string from left to right and If a character repeats, compare its leftmost index with the current result
- Update the result if the result is greater.
Below is the implementation of the above approach:
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;
}
// 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
# 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
// 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
<script>
// Javascript program to find first repeating character
let NO_OF_CHARS = 256;
/* The function returns index of the first
repeating character in a string. If
all characters are repeating then
returns -1 */
function firstRepeating(str)
{
// Initialize leftmost index of every
// character as -1.
let firstIndex = new Array(NO_OF_CHARS);
for (let 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.
let res = Number.MAX_VALUE;
for (let i = 0; i < str.length; i++)
{
if (firstIndex[str[i].charCodeAt()] == -1)
{
firstIndex[str[i].charCodeAt()] = i;
}
else
{
res = Math.min(res, firstIndex[str[i].charCodeAt()]);
}
}
return (res == Number.MAX_VALUE) ? -1 : res;
}
let str = "geeksforgeeks".split('');
let index = firstRepeating(str);
if (index == -1)
{
document.write("Either all characters are "
+ "distinct or string is empty");
}
else
{
document.write("First Repeating character is " + str[index]);
}
// This code is contributed by decode2207.
</script>
OutputFirst Repeating character is g
Time Complexity: O(N). Traversing string one time
Auxiliary Space: O(1)
Repeated Character Whose First Appearance is Leftmost by Reverse Traversal:
The idea is to track the characters which have encountered while traversing from right to left. Whenever a character is already repeated then take that index to our answer.
Follow the steps to solve the problem:
- Initialise an array visited of size 256 which keeps track of characters that have been encountered.
- Traverse string from right to left and If a character repeats, add that index to the result.
Below is the implementation of the above approach:
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;
}
// 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
# 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
// 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
<script>
// Javascript program to find first repeating character
let NO_OF_CHARS = 256;
/* The function returns index of the first
repeating character in a string. If
all characters are repeating then
returns -1 */
function firstRepeating(str)
{
// Mark all characters as not visited
let visited = new Array(NO_OF_CHARS);
for (let i = 0; i < NO_OF_CHARS; i++)
visited[i] = false;
// Traverse from right and update res as soon
// as we see a visited character.
let res = -1;
for (let i = str.length - 1; i >= 0; i--)
{
if (visited[str[i].charCodeAt()] == false)
visited[str[i].charCodeAt()] = true;
else
res = i;
}
return res;
}
let str = "geeksforgeeks";
let index = firstRepeating(str);
if (index == -1)
document.write("Either all characters are " +
"distinct or string is empty");
else
document.write("First Repeating character" +
" is " + str[index]);
// This code is contributed by divyeshrabadiya07.
</script>
OutputFirst Repeating character is g
Time Complexity: O(N). Traversing string one time
Auxiliary Space: O(1)
Discussed more approaches in Find repeated character present first in a string.
Similar Reads
Basics & Prerequisites
Data Structures
Array Data StructureIn this article, we introduce array, implementation in different popular languages, its basic operations and commonly seen problems / interview questions. An array stores items (in case of C/C++ and Java Primitive Arrays) or their references (in case of Python, JS, Java Non-Primitive) at contiguous
3 min read
String in Data StructureA string is a sequence of characters. The following facts make string an interesting data structure.Small set of elements. Unlike normal array, strings typically have smaller set of items. For example, lowercase English alphabet has only 26 characters. ASCII has only 256 characters.Strings are immut
2 min read
Hashing in Data StructureHashing is a technique used in data structures that efficiently stores and retrieves data in a way that allows for quick access. Hashing involves mapping data to a specific index in a hash table (an array of items) using a hash function. It enables fast retrieval of information based on its key. The
2 min read
Linked List Data StructureA linked list is a fundamental data structure in computer science. It mainly allows efficient insertion and deletion operations compared to arrays. Like arrays, it is also used to implement other data structures like stack, queue and deque. Here’s the comparison of Linked List vs Arrays Linked List:
2 min read
Stack Data StructureA Stack is a linear data structure that follows a particular order in which the operations are performed. The order may be LIFO(Last In First Out) or FILO(First In Last Out). LIFO implies that the element that is inserted last, comes out first and FILO implies that the element that is inserted first
2 min read
Queue Data StructureA Queue Data Structure is a fundamental concept in computer science used for storing and managing data in a specific order. It follows the principle of "First in, First out" (FIFO), where the first element added to the queue is the first one to be removed. It is used as a buffer in computer systems
2 min read
Tree Data StructureTree Data Structure is a non-linear data structure in which a collection of elements known as nodes are connected to each other via edges such that there exists exactly one path between any two nodes. Types of TreeBinary Tree : Every node has at most two childrenTernary Tree : Every node has at most
4 min read
Graph Data StructureGraph Data Structure is a collection of nodes connected by edges. It's used to represent relationships between different entities. If you are looking for topic-wise list of problems on different topics like DFS, BFS, Topological Sort, Shortest Path, etc., please refer to Graph Algorithms. Basics of
3 min read
Trie Data StructureThe Trie data structure is a tree-like structure used for storing a dynamic set of strings. It allows for efficient retrieval and storage of keys, making it highly effective in handling large datasets. Trie supports operations such as insertion, search, deletion of keys, and prefix searches. In this
15+ min read
Algorithms
Searching AlgorithmsSearching algorithms are essential tools in computer science used to locate specific items within a collection of data. In this tutorial, we are mainly going to focus upon searching in an array. When we search an item in an array, there are two most common algorithms used based on the type of input
2 min read
Sorting AlgorithmsA Sorting Algorithm is used to rearrange a given array or list of elements in an order. For example, a given array [10, 20, 5, 2] becomes [2, 5, 10, 20] after sorting in increasing order and becomes [20, 10, 5, 2] after sorting in decreasing order. There exist different sorting algorithms for differ
3 min read
Introduction to RecursionThe process in which a function calls itself directly or indirectly is called recursion and the corresponding function is called a recursive function. A recursive algorithm takes one step toward solution and then recursively call itself to further move. The algorithm stops once we reach the solution
14 min read
Greedy AlgorithmsGreedy algorithms are a class of algorithms that make locally optimal choices at each step with the hope of finding a global optimum solution. At every step of the algorithm, we make a choice that looks the best at the moment. To make the choice, we sometimes sort the array so that we can always get
3 min read
Graph AlgorithmsGraph is a non-linear data structure like tree data structure. The limitation of tree is, it can only represent hierarchical data. For situations where nodes or vertices are randomly connected with each other other, we use Graph. Example situations where we use graph data structure are, a social net
3 min read
Dynamic Programming or DPDynamic Programming is an algorithmic technique with the following properties.It is mainly an optimization over plain recursion. Wherever we see a recursive solution that has repeated calls for the same inputs, we can optimize it using Dynamic Programming. The idea is to simply store the results of
3 min read
Bitwise AlgorithmsBitwise algorithms in Data Structures and Algorithms (DSA) involve manipulating individual bits of binary representations of numbers to perform operations efficiently. These algorithms utilize bitwise operators like AND, OR, XOR, NOT, Left Shift, and Right Shift.BasicsIntroduction to Bitwise Algorit
4 min read
Advanced
Segment TreeSegment Tree is a data structure that allows efficient querying and updating of intervals or segments of an array. It is particularly useful for problems involving range queries, such as finding the sum, minimum, maximum, or any other operation over a specific range of elements in an array. The tree
3 min read
Pattern SearchingPattern searching algorithms are essential tools in computer science and data processing. These algorithms are designed to efficiently find a particular pattern within a larger set of data. Patten SearchingImportant Pattern Searching Algorithms:Naive String Matching : A Simple Algorithm that works i
2 min read
GeometryGeometry is a branch of mathematics that studies the properties, measurements, and relationships of points, lines, angles, surfaces, and solids. From basic lines and angles to complex structures, it helps us understand the world around us.Geometry for Students and BeginnersThis section covers key br
2 min read
Interview Preparation
Practice Problem