Java program to Find First non repeating character in a String
Java Program to find the First non repeating character in a string
In this article, we will learn how to code a java program to find the first non repeating character in a string
Method discussed
- Method 1 – Using indexOf() and lastIndexOf() methods
- Method 2 – This method builds a frequency array
- Method 3 – This method uses Linked Hashmap
- Method 4 – This method uses Set and ArrayList
- Method 5 – This method uses Java 8
Method 1
Using indexOf() and lastIndexOF() methods.
As soon as we find the first item that only appears once print stop further.
Run
class Main
{
public static void main(String args[])
{
String inputStr ="prepinsta";
boolean flag = true;
for(char i :inputStr.toCharArray())
{
// if current character is the last occurrence in the string
if (inputStr.indexOf(i) == inputStr.lastIndexOf(i))
{
System.out.println("First non-repeating character is: "+ i);
flag = false;
break;
}
}
if(flag)
System.out.println("There is no non repeating character in input string");
}
}
Output
First non-repeating character is: r
Method 2
- This method builds a frequency array
- With a frequency count of each ASCII character between 0 – 255
- We then find iterate the input string from the start
- Print the first character with frequency count == 1
class Main {
static final int NO_OF_CHARS = 256;
static char count[] = new char[NO_OF_CHARS];
// this method builds count array which updates frequency for each
// ascii character (0-255)
// example for 'p' ascii value is 112, in the array
// count[112] value would be 2 (p appears twice)
static void buildCharCountArray(String str)
{
for (int i = 0; i < str.length(); i++) {
count[str.charAt(i)]++;
}
}
// this method finds first non repeating character
// returns the index of the first non repeating character
static int findFirstNonRepeating(String string)
{
// build char count array
buildCharCountArray(string);
int pos = -1, i;
for (i = 0; i < string.length(); i++) {
if (count[string.charAt(i)] == 1) {
pos = i;
break;
}
}
return pos;
}
// Driver method
public static void main(String[] args)
{
String string = "prepinsta";
int pos = findFirstNonRepeating(string);
System.out.println(
pos == -1
? "All characters are repeating "
: "First non-repeating character is "
+ string.charAt(pos));
}
}Output
First non-repeating character is: r
Method 3
This method uses Linked Hashmap
Run
import java.util.*;
import java.util.Map.Entry;
class Main {
public static void main(String[] args)
{
String string = "prepinsta";
char ch = findFirstNonRepeating(string);
System.out.println("First non-repeating character is : " + ch);
}
public static Character findFirstNonRepeating(String str)
{
HashMap charhashtable =
new LinkedHashMap();
int len;
Character ch;
len = str.length(); // Scan string and build hash table
for (int i = 0; i < len; i++)
{
ch = str.charAt(i);
if(charhashtable.containsKey(ch))
// increment count corresponding to ch
charhashtable.put(ch, charhashtable.get(ch) + 1);
else
charhashtable.put(ch , 1);
}
for(Entry entry: charhashtable.entrySet())
{
if(entry.getValue() == 1)
return entry.getKey();
}
return null;
}
}
Output
First non-repeating character is: r
Method 4
This method uses Set and ArrayList
Run
import java.util.*;
class Main {
public static Character findFirstNonRepeating(String str)
{
// set stores characters that are repeating
Set charRepeatingSet = new HashSet<>();
// ArrayList stores characters that are non repeating
List charNonRepeatingList = new ArrayList<>();
for(int i=0; i < str.length(); i++)
{
char ch = str.charAt(i);
// if set already contains character ch
if(charRepeatingSet.contains(ch))
continue;
// if Array List contains character ch
// remove existing ch from ArrayList and
// add ch to set
if(charNonRepeatingList.contains(ch)) {
charNonRepeatingList.remove((Character) ch);
charRepeatingSet.add(ch);
}
// else add to ArrayList as character must be first occurrence
else {
charNonRepeatingList.add(ch);
}
}
return charNonRepeatingList.get(0);
}
public static void main(String[] args)
{
String string = "prepinsta";
char ch = findFirstNonRepeating(string);
System.out.println("The first non repeated character is : " + ch);
}
}
Output
First non-repeating character is: r
Method 5
This method uses Java 8
Run
import java.util.*;
class Main {
public static Character findFirstNonRepeating(String string) {
Map map = new LinkedHashMap();
for (Character ch : string.toCharArray()) {
map.put(ch, map.containsKey(ch) ? map.get(ch) + 1 : 1);
}
return map.entrySet().stream().filter(x -> x.getValue() == 1).findFirst().get().getKey();
}
public static void main(String[] args)
{
String string = "prepinsta";
char character = findFirstNonRepeating(string);
System.out.println("First non-repeating character is : " + character);
}
}
Output
First non-repeating character is: r
Algorithm :
- Take String as a input from the user.
- Create array of 256 element to store frequency of each character.
- Iterate a loop from 0 to length of the string to calculate frequency of each character.
- Again iterate a loop from 0 to 256 to find the character whose frequency is 1 and also print that character.
- we will get the desired output.
Solution in Java for finding the non repeating characters in a string
Run
class Main
{
public static void main(String args[])
{
String inputStr ="prepinsta";
boolean flag = true;
for(char i :inputStr.toCharArray())
{
// if current character is the last occurrence in the string
if (inputStr.indexOf(i) == inputStr.lastIndexOf(i))
{
System.out.println("First non-repeating character is: "+ i);
flag = false;
break;
}
}
if(flag)
System.out.println("There is no non repeating character in input string");
}
}
Output :
Enter the string
prepinsta
The non repeating characters are :
a e i n r s t
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import java.util.*;
class Nonrepeat{
public static void main(String[] args)
{
Scanner sc=new Scanner(System.in);
String s=sc.nextLine();
StringBuilder sb=new StringBuilder(s);
//char[] c=s.toCharArray();
int flag;
for(int i=0;i<sb.length();i++)
{
flag=0;
for(int j=i+1;j<sb.length();j++)
{
if(sb.charAt(i)==sb.charAt(j)){
flag=1;
sb.deleteCharAt(j);
}
}
if(flag==0)
System.out.print(sb.charAt(i));
else
continue;
}
}}
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public class NonReapChars {
public static void main(String args[]) {
Scanner sc = new Scanner(System.in);
String str =sc.nextLine();
char[] chars=str.toCharArray();
int flag=0;
for(int i =0; i<chars.length; i++) {
flag=0;
for(int j=i+1; j<chars.length; j++) {
if(chars[i]==chars[j]) {
flag=1;
}
}
if(flag==0) {
System.out.println(chars[i]);
break;
}
}
}
}
import java.util.*;
public class Main
{
public static void main(String[] args)
{
Scanner sc=new Scanner(System.in);
String s=sc.nextLine();
char c[]=s.toCharArray();
int count=0;
for(int i=0;i<c.length;i++)
{
count=0;
for(int j=i+1;j0)
{
c[i]=’0′;
}
}
for(int i=0;i<c.length;i++)
{
if(c[i]!='0'&& c[i]!=' ')
{
System.out.println(c[i]);
break;
}
}
}
}