Count words in a given string

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.

Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

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.

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My Personal Notes

Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

C++

C

Java

Python3

C#

PHP

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