Logic to get the first non-repeating(distinct) character from the string

Question

In c# i want to create logic that if i a string like abcabda is passed to a method then it should return first non repeative character from string like in above it should return c. i am unable to convert a string to array of character then how to make comparison of each array character to the string and return the first non repeative character.

CanI make it like this?

class A
{
    static void main()
    {
        A a=new A();
        char  ch=a.m1(abcabd);
    }
}

class B
{
    char m1(string s)
    {
        string s1=s;
        char[] ch1=new char[s.length];
        for(int x=0; x<s.length;x++)
        {
            ch1[x]=s[x];
        }
        for(int x=0; x<s.length; x++)
        {
            for(int y=0; y<s.lenth; y++)
            {
                if(s[x]=ch1[y])
                {             
/// here i am confused how to create logic for comparison please let me know
// and how to return the character
                }
            }
        }
    }
}

Answer 1

It seems that you are looking for the first char in the string with its count equals to 1?

using System.Linq;
string str = "abcabda";
char result = str.FirstOrDefault(ch => str.IndexOf(ch) == str.LastIndexOf(ch));

Non LINQ version:

    for (int index = 0; index < str.Length; index++)
    {
        if (str.LastIndexOf(str[index]) == str.IndexOf(str[index]))
        {
            result = str[index];
            break;
        }
    }

Answer 2

You could use a bit of LINQ:

char result = input
    .GroupBy(c => c)             // group the characters
    .Where(g => g.Count() == 1)  // filter out groups with only 1 occurence
    .Select(g => g.Key)          // get the character from each remaining group
    .First();                    // return the first one

Answer 3

how about using LINQ?

string test = "abcabda";

var selectedChars = (from c in test.ToCharArray() 
                    group c by c into groups
                    where groups.Count() == 1
                    select groups).First();

This will return 'c' as per the example given in the question.

Answer 4

Pretty simple but:

    private char? findNonRepeat(string search)
    {
        foreach(char chr in search)
        {
            if (search.LastIndexOf(chr) == search.IndexOf(chr))
                return chr;
        }

        return null;
    }

Answer 5

This may not be the most efficient, but it works and is easy to read:

    public string FirstNonRepeatingChar(string inString)
    {
        var array = inString.ToCharArray();
        foreach (char distinctChar in array.Distinct())
        {
            if (array.Count(x => x == distinctChar) == 1)
                return distinctChar.ToString();
        }
        return null; //none
    }

Answer 6

I think you need to loop twice through the list of characters:

1. Once to build a Dictionary<char, int> of character-counts,
2. Then to find the first character in the string whose count equals 1

Answer 7

Here's your code so far:

char m1(string s) 
{ 
    string s1=s; 
    char[] ch1=new char[s.length]; 
    for(int x=0; x<s.length;x++) 
    { 
        ch1[x]=s[x]; 
    } 
    for(int x=0; x<s.length; x++) 
    { 
        for(int y=0; y<s.lenth; y++) 
        { 
            if(s[x]=ch1[y]) 
            {              
/// here i am confused how to create logic for comparison please let me know 
// and how to return the character 
            } 
        } 
    } 
} 

You're actually pretty close. I'm going to ignore all the stylistic problems and redundancies because they're not what you're asking about.

What you really want to do is step through your string character-by-character and see if that character exists later on in the string. If the character repeats, you can stop looking for it and go on to the next one. If you get to the end of the string without finding a repeat, you have found a non-duplicate character and can return it. You have most of the logic in your nested x/y loops, but are missing a few things:

    for(int x=0; x<s.length; x++) 
    {
        // you need a flag here to indicate whether your character is a duplicate
        for(int y=0; y<s.lenth; y++) // this loop should start at x+1, not 0
        { 
            if(s[x]=ch1[y]) // you need == instead of =
            {              
                // if you've gotten here, you have a duplicate --
                // set your flag to true and break out of the loop
            }
        }
        // at this point you should check your flag and
        // if it's not set, return your character: s[x]
    }

EDIT: You mentioned that you want to be able to find the string's length without calling Length, and presumably without naming any other methods. The way to do this is to use a foreach loop to iterate over the characters in the string, incrementing a counter as you go. Here is some code with comments for you to fill in:

// initialize counter to 0
foreach (char ch in s)
{
    // increment counter by 1
}
// now counter is the length of the string

Answer 8

Here is my solution

    public static char FirstNonRepeatedChar(string input)
    {
        bool isDuplicate;
        for (int i = 0; i < input.Length; i++)
        {
             isDuplicate = false;

            for (int j = 0; j < input.Length; j++)
            {
                if ((input[i] == input[j]) && i !=j )
                {
                    isDuplicate = true;
                    break;
                }

            }
            if (!isDuplicate)
            {
                return input[i];
            }

        }
        return default(char);

    }

Answer 9

"string".ToCharArray() would give you an array containing characters that make "string"

Answer 10

Three ways to find first non repeating character in a string c#

find the code below -

public char firstNonRepetitive(string inputString)
{
 int nextOccurrence = 0;
 char firstDistinctChar = ' ';
 for (int i = 0; i < inputString.Length; i++)
 {
    nextOccurrence = 0;
    for (int j = (i + 1); j < inputString.Length; j++)
    {
        if (inputString[i] == inputString[j])
            nextOccurrence++;
    }
    if (nextOccurrence == 0)
    {
        firstDistinctChar = inputString[i];
        break;
    }
  }
  return firstDistinctChar;

}

Check out amazing two more way -

program to find first non repeating character in a string c# - three ways

Answer 11

Here is the O(n) solution for this problem.

public static char FirstNonRepeatedChar(string inputString)
    {
        if (String.IsNullOrEmpty(inputString))
            return '\0';
        if (inputString.Length == 1)
            return inputString[0];

        Hashtable charTable = new Hashtable();
        for (int i = 0; i <= (inputString.Length - 1); i++)
        {
            if (charTable.Contains(inputString[i]))
            {
                int currentCount = Int16.Parse(charTable[inputString[i]].ToString());
                charTable[inputString[i]] = currentCount + 1;
            }
            else
                charTable.Add(inputString[i], 1);
        }
        for (int i = 0; i <= (inputString.Length - 1); i++)
        {
            if (charTable[inputString[i]].ToString() == "1")
            {
                return char.Parse(inputString[i].ToString());
            }
        }
        return '\0';
    }

Answer 12

To read each character in a string is as simple as:

foreach (Char character in myString)
{

}

Answer 13

one possible solution: take each character from the string from right to left. for each char, check for any other occurence of the character in the string. if there is no other occurence of the char in the string, add it to a stack. once you have done this to all the chars in the string, the top of the stack would contain the first non-repetitive character.

Answer 14

Here is a simple logic to get first non repeating character from a string

Example : AABBCCdEEfGG , here the first no repeating char is "d"

namespace PurushLogics
{
    class Purush_FirstNonRepeatingChar
    {
        public static void Main()
        {
            string inputString = "AABBCCdEEfGG";
            int i = 0;
            char[] a = inputString.ToCharArray();
            bool repeat = false;
            for (i = 0; i < a.Length; )
            {

                for (int j = i + 1; j < a.Length; )
                {
                    if (a[i] == a[j])
                    {
                        a = a.Where(w => w != a[i]).ToArray(); // Will return the array removing/deleting the character that is in a[i] location
                        repeat = true;
                        break;
                    }
                    else
                    {

                        repeat = false;
                    }

                    break;
                }

                if (repeat == false || a.Length == 1)
                {
                    break;
                }
            }
            Console.WriteLine(a[i]);
            Console.ReadKey();
        }
    }
}

Answer 15

Time Complexity O(n) solution :

public static char GetNonRepeatingFirstCharacter(string str)
    {
        char firstNonRepeatingChar = default(char);
        if(!string.IsNullOrWhiteSpace(str))
        {
            // as we are dealing with lowercase letter and array index is starting from ZERO
            // we are taking the ASCII value of character 'a' which is 97 
            // so that we can assign if the character is 'a' we can assign to the index zero of array.
            int asciiOfInitialChar = 'a';

            // array index 26 as we have only 26 alphabet. 
            int[] alphabetArray = new int[26];

            // loop through the string provided. 
            // O(n) as it loops till the length of the array.
            foreach (var ch in str)
            {
                // checking if the array contains only lowercase character else throw format exception.
                if (ch < 97 || ch > 122)
                {
                    throw new FormatException("Given string contain non lowercase alphabet");
                }

                // subtracting with 97 so we can assign 'a' to index 0 and b to index 1 so on..
                var index = ch - asciiOfInitialChar;
                // incrementing the count so that we can get to know how many character is there in a string
                alphabetArray[ch - asciiOfInitialChar]++;
            }

            // fixed looping, can be considered as O(1) as it is always loop 26 times irrespective of length of the array
            for (int i = 0; i < 26; i++)
            {
                //finding first non repeating character as we have count of the characters in the alphabetArray
                if (alphabetArray[i] == 1)
                {
                    // converting to character by adding the asciiOfinitialChar 97 
                    // so that we will get if the index is 1 then 1 + 97 = 98  which is the ASCII vale of character 'b'
                    // break the loop as we found first non repeating character
                    firstNonRepeatingChar = (char)(i + asciiOfInitialChar);
                    break;
                }
            }


        }

        return firstNonRepeatingChar;
    }

Solution with unit test case:

GitHub: solution with unit test

Answer 16

The logic will give you the first non repetitive character of string, if you want to get the index of that char from string just replace 'a.indexOf(x)'with 'x' in Sysop.

package practice.learning;

import java.util.Scanner; public class FirstRepetitiveTwo {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Scanner sc=new Scanner(System.in);
    
    String a=sc.nextLine();
    int count=0;
    char x=' ';
    for(int i=0;i<=a.length()-1;i++) {
        x=a.charAt(i);
        for(int j=0;j<=a.length()-1;j++) {
            if(x==a.charAt(j)) {
                count++;
                }
        }
        if(count==1) {
            break;
        }
        count=0;
    }
    System.out.println(x);  
}

}