Count words in a given string

Difficulty Level : Easy
Last Updated : 06 Nov, 2020

Given a string, count number of words in it. The words are separated by following characters: space (‘ ‘) or new line (‘\n’) or tab (‘\t’) or a combination of these.

There can be many solutions to this problem. Following is a simple and interesting solution.
The idea is to maintain two states: IN and OUT. The state OUT indicates that a separator is seen. State IN indicates that a word character is seen. We increment word count when previous state is OUT and next character is a word character.

C++

/* C++ program to count no of words  
from given input string. */
#include <bits/stdc++.h> 
using namespace std;  
  
#define OUT 0  
#define IN 1  
  
// returns number of words in str  
unsigned countWords(char *str)  
{  
    int state = OUT;  
    unsigned wc = 0; // word count  
  
    // Scan all characters one by one  
    while (*str)  
    {  
        // If next character is a separator, set the  
        // state as OUT  
        if (*str == ' ' || *str == '\n' || *str == '\t')  
            state = OUT;  
  
        // If next character is not a word separator and  
        // state is OUT, then set the state as IN and  
        // increment word count  
        else if (state == OUT)  
        {  
            state = IN;  
            ++wc;  
        }  
  
        // Move to next character  
        ++str;  
    }  
  
    return wc;  
}  
  
// Driver code 
int main(void)  
{  
    char str[] = "One two     three\n four\tfive ";  
    cout<<"No of words : "<<countWords(str);  
    return 0;  
}  
  
// This is code is contributed by rathbhupendra 

C

/* C program to count no of words from given input string. */
#include <stdio.h> 
  
#define OUT    0 
#define IN    1 
  
// returns number of words in str 
unsigned countWords(char *str) 
{ 
    int state = OUT; 
    unsigned wc = 0;  // word count 
  
    // Scan all characters one by one 
    while (*str) 
    { 
        // If next character is a separator, set the  
        // state as OUT 
        if (*str == ' ' || *str == '\n' || *str == '\t') 
            state = OUT; 
  
        // If next character is not a word separator and  
        // state is OUT, then set the state as IN and  
        // increment word count 
        else if (state == OUT) 
        { 
            state = IN; 
            ++wc; 
        } 
  
        // Move to next character 
        ++str; 
    } 
  
    return wc; 
} 
  
// Driver program to tes above functions 
int main(void) 
{ 
    char str[] = "One two         three\n    four\tfive  "; 
    printf("No of words : %u", countWords(str)); 
    return 0; 
} 

Java

/* Java program to count no of words 
from given input string. */
public class GFG { 
   
    static final int OUT = 0; 
    static final int IN = 1; 
       
    // returns number of words in str 
    static int countWords(String str) 
    { 
        int state = OUT; 
        int wc = 0;  // word count 
        int i = 0; 
          
        // Scan all characters one by one 
        while (i < str.length()) 
        { 
            // If next character is a separator, set the  
            // state as OUT 
            if (str.charAt(i) == ' ' || str.charAt(i) == '\n' 
                    || str.charAt(i) == '\t') 
                state = OUT; 
                  
       
            // If next character is not a word separator 
            // and state is OUT, then set the state as IN 
            // and increment word count 
            else if (state == OUT) 
            { 
                state = IN; 
                ++wc; 
            } 
       
            // Move to next character 
            ++i; 
        } 
        return wc; 
    } 
       
    // Driver program to test above functions 
    public static void main(String args[]) 
    { 
        String str = "One two       three\n four\tfive  "; 
        System.out.println("No of words : " + countWords(str)); 
    } 
} 
// This code is contributed by Sumit Ghosh 

Python3

# Python3 program to count words  
# in a given string 
OUT = 0
IN = 1
  
# Returns number of words in string 
def countWords(string): 
    state = OUT 
    wc = 0
  
    # Scan all characters one by one 
    for i in range(len(string)): 
  
        # If next character is a separator,  
        # set the state as OUT 
        if (string[i] == ' ' or string[i] == '\n' or
            string[i] == '\t'): 
            state = OUT 
  
        # If next character is not a word  
        # separator and state is OUT, then  
        # set the state as IN and increment  
        # word count 
        elif state == OUT: 
            state = IN 
            wc += 1
  
    # Return the number of words 
    return wc 
  
# Driver Code 
string = "One two         three\n four\tfive "
print("No. of words : " + str(countWords(string))) 
  
# This code is contributed by BHAVYA JAIN 

C#

// C# program to count no of words 
// from given input string.  
using System; 
  
class GFG { 
      
    static int OUT = 0; 
    static int IN = 1; 
      
    // returns number of words in str 
    static int countWords(String str) 
    { 
        int state = OUT; 
        int wc = 0; // word count 
        int i = 0; 
          
        // Scan all characters one  
        // by one 
        while (i < str.Length) 
        { 
            // If next character is a separator,  
            // set the state as OUT 
            if (str[i] == ' ' || str[i] == '\n'||  
                                  str[i] == '\t') 
                state = OUT; 
                  
      
            // If next character is not a word  
            // separator and state is OUT, then  
            // set the state as IN and increment 
            // word count 
            else if (state == OUT) 
            { 
                state = IN; 
                ++wc; 
            } 
      
            // Move to next character 
            ++i; 
        } 
          
        return wc; 
    } 
      
    // Driver program to test above functions 
    public static void Main() 
    { 
        String str = "One two     three\n four\tfive "; 
        Console.WriteLine("No of words : "
                              + countWords(str)); 
    } 
} 
  
// This code is contributed by Sam007. 

PHP

<?php  
// PHP program to count no of  
// words from given input string 
$OUT = 0; 
$IN = 1; 
  
// returns number of words in str 
function countWords($str) 
{ 
    global $OUT, $IN; 
    $state = $OUT; 
    $wc = 0; // word count 
    $i = 0; 
      
    // Scan all characters one by one 
    while ($i < strlen($str)) 
    { 
        // If next character is  
        // a separator, set the  
        // state as OUT 
        if ($str[$i] == " " ||  
            $str[$i] == "\n" ||  
            $str[$i] == "\t") 
            $state = $OUT; 
  
        // If next character is not a  
        // word separator and state is  
        // OUT, then set the state as  
        // IN and increment word count 
        else if ($state == $OUT) 
        { 
            $state = $IN; 
            ++$wc; 
        } 
  
        // Move to next character 
        ++$i; 
    } 
  
    return $wc; 
} 
  
// Driver Code 
$str = "One two         three\n four\tfive "; 
echo "No of words : " . countWords($str); 
  
// This code is contributed 
// by ChitraNayal 
?> 

Output

No of words : 5

Time complexity: O(n)
This article is compiled by Narendra Kangralkar. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

Method 2: using String.split() method

Get the string to count the total number of words.
Check if the string is empty or null then return 0.
Use split() method of String class to split the string on whitespaces.
The split() method breaks the given string around matches of the given regular expression and returns an array of string.
The length of the array is the number of words in the given string.
Now, print the result.

Below is the implementation of the above approach:

Java

// Java program to count total 
// number of words in the string 
class GFG  
{ 
      
    // Function to count total number 
    // of words in the string 
    public static int 
      countWords(String str) 
    { 
          
        // Check if the string is null 
        // or empty then return zero 
        if (str == null || str.isEmpty()) 
            return 0; 
          
        // Splitting the string around 
        // matches of the given regular 
        // expression 
        String[] words = str.split("\\s+"); 
          
        // Return number of words 
        // in the given string 
        return words.length; 
    } 
      
    // Driver Code 
    public static void main(String args[]) 
    { 
          
        // Given String str 
        String str =  
          "One two       three\n four\tfive "; 
          
        // Print the result 
        System.out.println("No of words : " + 
           countWords(str)); 
    } 
} 
// This code is contributed by Prashant Srivastava

Output

No of words : 5

Time Complexity: O(N)

Method 3: using StringTokenizer.countTokens() method

Get the string to count the total number of words.
Check if the string is empty or null then return 0.
Create a StringTokenizer with the given string passed as a parameter.
Count the total number of words in the given string using the countTokens() method.
Now, print the result.

Below is the implementation of the above approach:

Java

// Java program to count total 
// number of words in the string 
import java.util.StringTokenizer; 
class GFG  
{ 
      
    // Function to count total number 
    // of words in the string 
    public static int 
      countWords(String str) 
    { 
          
        // Check if the string is null 
        // or empty then return zero 
        if (str    == null || str.isEmpty()) 
            return 0; 
          
        // Create a StringTokenizer with the  
        // given string passed as a parameter 
        StringTokenizer tokens = new 
          StringTokenizer(str); 
          
        // Return the number of words 
        // in the given string using 
        // countTokens() method 
        return tokens.countTokens(); 
    } 
      
    // Driver Code 
    public static void main(String args[]) 
    { 
          
        // Given String str 
        String str =  
          "One two       three\n four\tfive "; 
          
        // Print the result 
        System.out.println("No of words: " + 
          countWords(str)); 
    } 
} 
// This code is contributed by Prashant Srivastava

Output

No of words: 5

Time Complexity: O(N)

Method 4: using Character.isLetter() method

Get the string to count the total number of words.
Check if the string is empty or null then return 0.
Converting the given string into a character array.
Check if the character is a letter and index of the character array doesn’t equal to the end of the line that means, it is a word and set isWord by true.
Check if the character is not a letter that means there is a space, then we increment the wordCount by one and set the isWord by false.
Check for the last word of the sentence and increment the wordCount by one.
Now, print the result.

Below is the implementation of the above approach:

Java

// Java program to count total 
// number of words in the string 
class GFG  
{ 
      
    // Function to count total number 
    // of words in the string 
    public static int 
      countWords(String str) 
    { 
          
        // Check if the string is null 
        // or empty then return zero 
        if(str    == null || str.isEmpty()) 
            return 0; 
          
        int wordCount = 0; 
          
        boolean isWord = false; 
        int endOfLine = str.length() - 1; 
          
        // Converting the given string  
        // into a character array 
        char[] ch = str.toCharArray(); 
          
        for (int i = 0; i < ch.length; i++) { 
              
            // Check if the character is a letter 
            // and index of character array doesn't 
            // equal to end of line that means, it is 
            // a word and set isWord by true 
            if (Character.isLetter(ch[i])  
                && i != endOfLine) 
                
                isWord = true; 
              
            // Check if the character is not a letter 
            // that means there is a space, then we 
            // increment the wordCount by one and set 
            // the isWord by false 
            else if (!Character.isLetter(ch[i])  
                     && isWord) { 
                
                wordCount++; 
                isWord = false; 
            } 
              
            // Check for the last word of the  
            // sentence and increment the wordCount  
            // by one 
            else if (Character.isLetter(ch[i]) 
                     && i == endOfLine) 
                wordCount++; 
        } 
          
        // Return the total number of  
        // words in the string 
        return wordCount; 
          
    } 
      
    // Driver Code 
    public static void main(String args[]) 
    { 
          
        // Given String str 
        String str =  
          "One two       three\n four\tfive "; 
          
        // Print the result 
        System.out.println("No of words : " + 
          countWords(str)); 
    } 
} 
// This code is contributed by Prashant Srivastava

Output

No of words : 5

Time Complexity: O(N)

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