Find the first repeated word in a string

// C# program to find first repeated word in a string
using System;
using System.Collections.Generic;

class GFG {
  static void solve(string s)
  {
    Dictionary<string, int> mp = new Dictionary<
      string, int>(); // to store occurrences of word
    string t = "";
    string ans = "";
    // traversing from back makes sure that we get the
    // word which repeats first as ans
    for (int i = s.Length - 1; i >= 0; i--) {
      // if char present , then add that in temp word
      // string t
      if (s[i] != ' ') {
        t += s[i];
      }
      // if space is there then this word t needs to
      // stored in map
      else {
        if (mp.ContainsKey(t)) {
          mp[t] += 1;
        }
        else {
          mp.Add(t, 1);
        }
        // if that string t has occurred previously
        // then it is a possible ans
        if (mp[t] > 1) {
          ans = t;
        }
        // set t as empty for again new word
        t = "";
      }
    }

    // first word like "he" needs to be mapped
    if (mp.ContainsKey(t)) {
      mp[t] += 1;
    }
    else {
      mp.Add(t, 1);
    }

    if (mp[t] > 1) {
      ans = t;
    }

    if (ans != "") {
      // reverse ans string as it has characters in
      // reverse order
      char[] charArray = ans.ToCharArray();
      Array.Reverse(charArray);
      Console.WriteLine(new string(charArray));
    }
    else {
      Console.Write("No Repetition\n");
    }
  }
  public static void Main()
  {
    string u
      = "Ravi had been saying that he had been there";
    string v = "Ravi had been saying that";
    string w = "he had had he";
    solve(u);
    solve(v);
    solve(w);
  }
}

// This code is contributed by Aarti_Rathi

// C# program for finding first repeated
// word in a string
using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;

class HelloWorld {
    
    // returns first repeated word
    public static string findFirstRepeated(string s)
    {
        // break string into tokens
        // and then each string into set
        // if a word appeared before appears
        // again, return the word and break

        string[] token = s.Split(" ");

        // hashmap for storing word and its count
        // in sentence
        Dictionary<string, int> setOfWords = new Dictionary<string,int>();

        // store all the words of string
        // and the count of word in map
        for (int i=0; i < token.Length; i++)
        {
            if (setOfWords.ContainsKey(token[i]) == true)
            {
                setOfWords[token[i]] = setOfWords[token[i]] + 1;
            }
            else 
            {
                // insert new word to map
                setOfWords.Add(token[i], 1);
            }
        }
        // traverse again from first word of string s
        // to check if count of word is greater than 1
        // either take a new stream or store the words
        // in array of strings in previous loop
        for (int i=0; i < token.Length; i++)
        {
            int count = setOfWords[token[i]];
            if (count > 1)
            {
                return token[i];
            }
        }
        return "NoRepetition";
    }    

    static void Main() {
        string s = "Ravi had been saying that he had been there";
        string firstWord = findFirstRepeated(s);
        if (firstWord != "NoRepetition")
            Console.WriteLine("First repeated word :: "  + firstWord);
        else
            Console.WriteLine("No Repitition");
    }
}

// The code is contributed by Nidhi goel. 

using System;
using System.Collections.Generic;

class Program
{
    static string FirstRepeatedWord(string sentence)
    {
        // Splitting the string into words
        List<string> words = new List<string>();
        int pos;
        while ((pos = sentence.IndexOf(' ')) != -1)
        {
            string word = sentence.Substring(0, pos);
            words.Add(word);
            sentence = sentence.Remove(0, pos + 1);
        }
        words.Add(sentence); // Add the last word

        // Calculating the frequency of each word
        Dictionary<string, int> frequency = new Dictionary<string, int>();
        foreach (string word in words)
        {
            if (!frequency.ContainsKey(word))
            {
                frequency[word] = 1;
            }
            else
            {
                frequency[word]++;
            }
        }

        // Traversing the list of words
        foreach (string word in words)
        {
            // Checking if the frequency is greater than 1
            if (frequency[word] > 1)
            {
                // Return the word
                return word;
            }
        }

        // If no repeated word is found
        return "No repeated word found";
    }

    static void Main()
    {
        string sentence = "Vikram had been saying that he had been there";
        Console.WriteLine(FirstRepeatedWord(sentence));
    }
}

// This code is contributed by shivamgupta0987654321

using System;
using System.Collections.Generic;

public class MainClass
{
    public static void Solve(string s)
    {
        int n = s.Length; // size of the string.
        Dictionary<string, int> mp = new Dictionary<string, int>(); // To store first occurrence of a word.
        string ans = "", t = "";
        int min_idx = int.MaxValue; // To get minimum occurrence in the given string.

        int i = 0, j = 0; // iterators. i -> initial index of a word, j -> final index of a word.

        // loop to traverse in a string and to find out each
        // repeated word whose occurrence is minimum.
        while (j <= n)
        {
            // If found an entire word then check if it is
            // repeated or not using Dictionary.
            if (j == n || s[j] == ' ')
            {
                if (!mp.ContainsKey(t))
                {
                    mp[t] = i + 1; // Store the first occurrence of a word.
                }
                else
                {
                    // If there is a repetition then check for minimum occurrence of the word.
                    if (min_idx > mp[t])
                    {
                        min_idx = mp[t];
                        ans = t;
                    }
                }

                // Shift the pointers.
                t = "";
                i = j + 1;
                j = i;
            }
            else
            {
                t += s[j];
                j++;
            }
        }

        // If ans is an empty string then this signifies that
        // there is no Repetition.
        if (ans == "")
        {
            Console.WriteLine("No Repetition");
        }
        else
        {
            Console.WriteLine(ans);
        }
    }

    public static void Main(string[] args)
    {
        string s1 = "Ravi had been saying that he had been there";
        string s2 = "Ravi had been saying that";
        string s3 = "he had had he";

        Solve(s1);
        Solve(s2);
        Solve(s3);
    }
}