Find the word from a given sentence having given word as prefix

Namachila November 18, 2025

0 1 6 minutes read

Given a string S representing a sentence and another string word, the task is to find the word from S which has the string word as a prefix. If no such word is present in the string, print -1.

Examples:

Input: S = “Welcome to Geeksforzambiatek”, word=”Gee”
Output: Geeksforzambiatek
Explanation:
The word “Geeksforzambiatek” in the sentence has the prefix “Gee”.

Input: s=”Competitive Programming”, word=”kdflk”
Output: -1
Explanation:
No word in the string has “kdflk” as its prefix.

Approach: Follow the steps below to find which word has the given prefix:

Extract the words from the sentence using the stringstream and store them in a vector of strings.
Now, traverse the array and check which word contains the given word as its own prefix.
If found to be true for any word, then print that word. Otherwise, if no such word is found, print -1.

Below is the implementation of the above approach:

C++

// C++ program for the above approach
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to find the position
// of the string having word as prefix
string isPrefixOfWord(string sentence,
                      string Word)
{
    stringstream ss(sentence);
 
    // Initialize a vector
    vector<string> v;
    string temp;
 
    // Extract words from the sentence
    while (ss >> temp) {
        v.push_back(temp);
    }
 
    // Traverse each word
    for (int i = 0; i < v.size(); i++) {
 
        // Traverse the characters of word
        for (int j = 0; j < v[i].size(); j++) {
 
            // If prefix does not match
            if (v[i][j] != Word[j])
                break;
 
            // Otherwise
            else if (j == Word.size() - 1)
 
                // Return  the word
                return v[i];
        }
    }
 
    // Return -1 if not present
    return "-1";
}
 
// Driver code
int main()
{
    string s = "Welcome to Geeksforzambiatek";
    string word = "Gee";
 
    cout << isPrefixOfWord(s, word) << endl;
    return 0;
}

Java

// Java program for the above approach 
import java.util.*;
import java.io.*;
import java.lang.Math;
 
class GFG{
      
// Function to find the position 
// of the string having word as prefix 
static String isPrefixOfWord(String sentence, 
                             String Word) 
{ 
    String a[] = sentence.split(" ");
   
    // Initialize an ArrayList 
    ArrayList<String> v = new ArrayList<>();
     
    // Extract words from the sentence 
    for(String e : a)
        v.add(e);
     
    // Traverse each word 
    for(int i = 0; i < v.size(); i++)
    { 
         
        // Traverse the characters of word 
        for(int j = 0; j < v.get(i).length(); j++)
        { 
             
            // If prefix does not match 
            if (v.get(i).charAt(j) != Word.charAt(j)) 
                break; 
                 
            // Otherwise 
            else if (j == Word.length() - 1) 
             
                // Return  the word 
                return v.get(i); 
        } 
    } 
     
    // Return -1 if not present 
    return "-1"; 
} 
 
// Driver code  
public static void main(final String[] args) 
{
    String s = "Welcome to Geeksforzambiatek"; 
    String word = "Gee"; 
   
    System.out.println(isPrefixOfWord(s, word));
}
}
 
// This code is contributed by bikram2001jha

Python3

# Python3 program for the 
# above approach
 
# Function to find the 
# position of the string 
# having word as prefix
def isPrefixOfWord(sentence, word):
   
    a=sentence.split(" ")
 
    # Initialize an List
    v = []
 
    # Extract words from 
    # the sentence
    for i in a:
        v.append(i)
 
    # Traverse each word 
    for i in range(len(v)):
 
        # Traverse the characters of word 
        for j in range(len(v[i])):
 
            # If prefix does not match
            if(v[i][j] != word[j]):
                break
 
            # Otherwise
            elif(j == len(word) - 1):
 
                # Return  the word
                return v[i]
 
    # Return -1 if not present
    return -1
 
# Driver code 
s = "Welcome to Geeksforzambiatek"
word = "Gee"
print(isPrefixOfWord(s, word))
 
# This code is contributed by avanitrachhadiya2155

C#

// C# program for the above approach 
using System;
using System.Collections.Generic;
class GFG{
      
// Function to find the position 
// of the string having word as prefix 
static String isPrefixOfWord(String sentence, 
                             String Word) 
{ 
  String []a = sentence.Split(' ');
 
  // Initialize an List 
  List<String> v = new List<String>();
 
  // Extract words from the sentence 
  foreach(String e in a)
    v.Add(e);
 
  // Traverse each word 
  for(int i = 0; i < v.Count; i++)
  { 
    // Traverse the characters of word 
    for(int j = 0; j < v[i].Length; j++)
    { 
      // If prefix does not match 
      if (v[i][j] != Word[j]) 
        break; 
 
      // Otherwise 
      else if (j == Word.Length - 1) 
 
        // Return  the word 
        return v[i]; 
    } 
  } 
 
  // Return -1 if not present 
  return "-1"; 
} 
 
// Driver code  
public static void Main(String[] args) 
{
  String s = "Welcome to Geeksforzambiatek"; 
  String word = "Gee"; 
  Console.WriteLine(isPrefixOfWord(s, word));
}
}
 
// This code is contributed by Rajput-Ji

Javascript

<script>
//Javascript  program for the above approach
 
// Function to find the position 
// of the string having word as prefix 
function isPrefixOfWord(sentence, Word) 
{ 
    var a = sentence.split(" ");
   
    // Initialize an ArrayList 
    var v = [];
     
    // Extract words from the sentence 
    //for(String e : a)
    for(var i=0;i<a.length;i++)
    {
        v.push(a[i]);
    }
    // Traverse each word 
    for(var i = 0; i < v.length; i++)
    { 
         
        // Traverse the characters of word 
        for(var j = 0; j < v[i].length; j++)
        { 
             
            // If prefix does not match 
            if (v[i].charAt(j) != Word[j]) 
                break; 
                 
            // Otherwise 
            else if (j == Word.length- 1) 
             
                // Return  the word 
                return v[i]; 
        } 
    } 
     
    // Return -1 if not present 
    return "-1"; 
} 
   
var s = "Welcome to Geeksforzambiatek"; 
var word = "Gee"; 
document.write(isPrefixOfWord(s, word));
 
//This code in contributed by SoumikMondal
</script>

Output:

Geeksforzambiatek

Time Complexity: O(L), where L denotes the length of the string S
Auxiliary Space: O(L)

Approach: Follow the steps below to find which word has the given prefix:

1. Using the split() function, to extract word from the sentences

2. We use in operator to check presence of substring

C++

#include <iostream>
#include <string>
#include <vector>
#include <sstream>
 
using namespace std;
 
string prefix(string sentence, string word)
{
   
    // Converting the string into an array of words 
  // using the stringstream and getline() method
    vector<string> l;
    stringstream ss(sentence);
    string temp;
    while (ss >> temp) {
        l.push_back(temp);
    }
 
    // Initializing the variable to store 
  // the last word containing the prefix
    string c = "-1";
 
    // Looping through each word in the array
    for (string i : l) 
    {
       
        // Checking if the prefix is a substring of 
      // the current word using the find() method
        if (i.find(word) != string::npos) {
            c = i;
        }
    }
 
    // Returning the last word containing the prefix or -1 if not found
    return c;
}
 
// Driver code
int main() {
    string s = "Welcome to Geeksforzambiatek";
    string word = "Gee";
 
    cout << prefix(s, word) << endl; // Outputs "Geeksforzambiatek"
 
    return 0;
}

Java

import java.util.*;
 
public class Main {
    static String prefix(String sentence, String word) {
        // Converting the string into an array of words using the split() method
        String[] l = sentence.split(" ");
 
        // Initializing the variable to store the last word containing the prefix
        String c = "-1";
 
        // Looping through each word in the array
        for (String i : l) {
            // Checking if the prefix is a substring of the current word using the contains() method
            if (i.contains(word)) {
                c = i;
            }
        }
 
        // Returning the last word containing the prefix or -1 if not found
        return c;
    }
 
    // Driver code
    public static void main(String[] args) {
        String s = "Welcome to Geeksforzambiatek";
        String word = "Gee";
 
        System.out.println(prefix(s, word)); // Outputs "Geeksforzambiatek"
    }
}

Python3

def prefix(sentence, word):
  # converting string into list
  l=sentence.split()
  c=-1
  for i in l:
    # in operator to check substring 
    if word in i:
      c=i
  # Returning the substring or -1
  return c
# input string 
s = "Welcome to Geeksforzambiatek"
#prefix 
word = "Gee"
print(prefix(s, word))
# This code is contributed by Asif shaik

C#

//C# code
using System;
 
public class Program
{
    // Function to return the last word that contains the given prefix
    static string Prefix(string sentence, string word)
    {
        // Converting the string into an array of words using the Split() method
        string[] l = sentence.Split(" ");
 
        // Initializing the variable to store the last word containing the prefix
        string c = "-1";
 
        // Looping through each word in the array
        foreach (string i in l)
        {
            // Checking if the prefix is a substring of the current word using the Contains() method
            if (i.Contains(word))
            {
                c = i;
            }
        }
 
        // Returning the last word containing the prefix or -1 if not found
        return c;
    }
 
    // Driver code
    public static void Main()
    {
        string s = "Welcome to Geeksforzambiatek";
        string word = "Gee";
 
        Console.WriteLine(Prefix(s, word)); // Outputs "Geeksforzambiatek"
    }
}

Javascript

function prefix(sentence, word) {
  // Converting the string into an array of words using the split() method
  let l = sentence.split(" ");
 
  // Initializing the variable to store the last word containing the prefix
  let c = -1;
 
  // Looping through each word in the array
  for (let i of l) {
    // Checking if the prefix is a substring of the current word using the includes() method
    if (i.includes(word)) {
      c = i;
    }
  }
 
  // Returning the last word containing the prefix or -1 if not found
  return c;
}
 
// Input string
let s = "Welcome to Geeksforzambiatek";
// Prefix
let word = "Gee";
 
console.log(prefix(s, word)); // Outputs "Geeksforzambiatek"

Output

Geeksforzambiatek

Time Complexity: O(L), where L denotes the length of the string S
Auxiliary Space: O(L)

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