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.

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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