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Remove extra spaces from a string

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Given a string containing many consecutive spaces, trim all spaces so that all words should contain only a single space between them. The conversion should be done in-place and solution should handle trailing and leading spaces and also remove preceding spaces before common punctuation like full stop, comma and a question mark.

Examples: 

Input: 
str = " Hello Geeks . Welcome to GeeksforGeeks . ";
Output:
"Hello Geeks. Welcome to GeeksforGeeks."
Input:
str = "GeeksforGeeks";
Output:
"GeeksforGeeks"
(No change is needed)

This problem is an extension of Remove spaces from a given string

Method 1:

  • The idea is to maintain 2 pointers. Initially both point to the beginning of the array.
  • The first pointer keeps track of next position to be filled in output string.
  • The second pointer is advanced to read all characters of the string one by one.
  • On finding any non-space character, the character is copied to the location of the first pointer and then both the first and second pointers are advanced.
  • If non-space character is a full stop, comma or a question mark, we also remove any preceding space before it.
  • On finding consecutive space characters, one only space is copied to the location of the first pointer and rest are ignored. The leading and trailing spaces are handled separately in the solution.

Below is C++ implementation of above idea.

C++




// C++ program to implement custom trim() function
#include <iostream>
using namespace std;
 
// Function to in-place trim all spaces in the
// string such that all words should contain only
// a single space between them.
void removeSpaces(string &str)
{
    // n is length of the original string
    int n = str.length();
 
    // i points to next position to be filled in
    // output string/ j points to next character
    // in the original string
    int i = 0, j = -1;
 
    // flag that sets to true is space is found
    bool spaceFound = false;
 
    // Handles leading spaces
    while (++j < n && str[j] == ' ');
 
    // read all characters of original string
    while (j < n)
    {
        // if current characters is non-space
        if (str[j] != ' ')
        {
            // remove preceding spaces before dot,
            // comma & question mark
            if ((str[j] == '.' || str[j] == ',' ||
                 str[j] == '?') && i - 1 >= 0 &&
                 str[i - 1] == ' ')
                str[i - 1] = str[j++];
 
            else
                // copy current character at index i
                // and increment both i and j
                str[i++] = str[j++];
 
            // set space flag to false when any
            // non-space character is found
            spaceFound = false;
        }
        // if current character is a space
        else if (str[j++] == ' ')
        {
            // If space is encountered for the first
            // time after a word, put one space in the
            // output and set space flag to true
            if (!spaceFound)
            {
                str[i++] = ' ';
                spaceFound = true;
            }
        }
    }
 
    // Remove trailing spaces
    if (i <= 1)
        str.erase(str.begin() + i, str.end());
    else
        str.erase(str.begin() + i - 1, str.end());
}
 
// Driver Code
int main()
{
    string str = "   Hello Geeks . Welcome   to"
                 "  GeeksforGeeks   .    ";
 
    removeSpaces(str);
 
    cout << str;
 
    return 0;
}


Java




class Main{
  public static String removeSpaces(String s) {
    int n = s.length();
    int i = 0, j = -1;
    boolean spaceFound = false;
     
    // Handles leading spaces
    while (j < n - 1 && s.charAt(j + 1) == ' ') {
        j++;
    }
     
    // read all characters of original string
    while (j < n) {
        // if current characters is non-space
        if (s.charAt(j) != ' ') {
            // remove preceding spaces before dot,
            // comma & question mark
            if ((s.charAt(j) == '.' || s.charAt(j) == ',' ||
                 s.charAt(j) == '?') && i - 1 >= 0 &&
                 s.charAt(i - 1) == ' ') {
                s = s.substring(0, i - 1) + s.charAt(j) + s.substring(i);
                j++;
            } else {
                // copy current character at index i
                // and increment both i and j
                s = s.substring(0, i) + s.charAt(j) + s.substring(i + 1);
                i++;
                j++;
            }
             
            // set space flag to false when any
            // non-space character is found
            spaceFound = false;
        } else if (s.charAt(j) == ' ') {
            // If space is encountered for the first
            // time after a word, put one space in the
            // output and set space flag to true
            if (!spaceFound) {
                s = s.substring(0, i) + ' ' + s.substring(i + 1);
                i++;
                spaceFound = true;
            }
            j++;
        }
    }
     
    // Remove trailing spaces
    if (i <= 1) {
        s = s.substring(0, i);
    } else {
        s = s.substring(0, i - 1);
    }
    return s;
}
 
// Driver code
public static void main(String[] args) {
    String str = "   Hello Geeks . Welcome   to"
            + "  GeeksforGeeks   .    ";
    str = removeSpaces(str);
    System.out.println(str);
}
 
   
}


Python3




# Python code for the above approach
 
def removeSpaces(s):
    # n is length of the original string
    n = len(s)
 
    # i points to next position to be filled in
    # output string/ j points to next character
    # in the original string
    i = 0
    j = -1
 
    # flag that sets to true is space is found
    spaceFound = False
 
    # Handles leading spaces
    while j < n - 1 and s[j + 1] == ' ':
        j += 1
 
    # read all characters of original string
    while j < n:
        # if current characters is non-space
        if s[j] != ' ':
            # remove preceding spaces before dot,
            # comma & question mark
            if ((s[j] == '.' or s[j] == ',' or
                 s[j] == '?') and i - 1 >= 0 and
                 s[i - 1] == ' '):
                s = s[:i - 1] + s[j] + s[i:]
                j += 1
 
            else:
                # copy current character at index i
                # and increment both i and j
                s = s[:i] + s[j] + s[i + 1:]
                i += 1
                j += 1
 
            # set space flag to false when any
            # non-space character is found
            spaceFound = False
        # if current character is a space
        elif s[j] == ' ':
            # If space is encountered for the first
            # time after a word, put one space in the
            # output and set space flag to true
            if not spaceFound:
                s = s[:i] + ' ' + s[i + 1:]
                i += 1
                spaceFound = True
 
            j += 1
 
    # Remove trailing spaces
    if i <= 1:
        s = s[:i]
    else:
        s = s[:i - 1]
 
    return s
 
 
# Driver Code
str = "   Hello Geeks . Welcome   to" \
      "  GeeksforGeeks   .    "
 
str = removeSpaces(str)
 
print(str)
 
 
# This code is contributed by adityasharmadev01


C#




// C# program to implement custom trim() function
using System;
 
public class Gfg
{
    public static void Main()
    {
        string str = "   Hello Geeks . Welcome   to" +
                     "  GeeksforGeeks   .    ";
 
        removeSpaces(ref str);
 
        Console.WriteLine(str);
    }
 
    // Function to in-place trim all spaces in the
    // string such that all words should contain only
    // a single space between them.
    public static void removeSpaces(ref string str)
    {
        // n is length of the original string
        int n = str.Length;
 
        // i points to next position to be filled in
        // output string/ j points to next character
        // in the original string
        int i = 0, j = -1;
 
        // flag that sets to true is space is found
        bool spaceFound = false;
 
        // Handles leading spaces
        while (++j < n && str[j] == ' ');
 
        // read all characters of original string
        while (j < n)
        {
            // if current characters is non-space
            if (str[j] != ' ')
            {
                // remove preceding spaces before dot,
                // comma & question mark
                if ((str[j] == '.' || str[j] == ',' ||
                     str[j] == '?') && i - 1 >= 0 &&
                     str[i - 1] == ' ')
                    str = str.Remove(i - 1, 1).Insert(i - 1, str[j++].ToString());
                else
                {
                    // copy current character at index i
                    // and increment both i and j
                    str = str.Remove(i, 1).Insert(i, str[j++].ToString());
                    i++;
                }
 
                // set space flag to false when any
                // non-space character is found
                spaceFound = false;
            }
            // if current character is a space
            else if (str[j++] == ' ')
            {
                // If space is encountered for the first
                // time after a word, put one space in the
                // output and set space flag to true
                if (!spaceFound)
                {
                    str = str.Remove(i, 0).Insert(i, " ");
                    i++;
                    spaceFound = true;
                }
            }
        }
 
        // Remove trailing spaces
        if (i <= 1)
            str = str.Remove(i, n - i);
        else
            str = str.Remove(i - 1, n - i + 1);
    }
}


Javascript




// JavaScript program to implement custom trim() function
 
// Function to in-place trim all spaces in the
// string such that all words should contain only
// a single space between them.
function removeSpaces(str) {
    // n is length of the original string
    let n = str.length;
     
    // i points to next position to be filled in
    // output string/ j points to next character
    // in the original string
    let i = 0, j = -1;
     
    // flag that sets to true is space is found
    let spaceFound = false;
     
    // Handles leading spaces
    while (++j < n && str[j] == ' ');
     
    // read all characters of original string
    while (j < n) {
        // if current characters is non-space
        if (str[j] != ' ') {
            // remove preceding spaces before dot,
            // comma & question mark
            if ((str[j] == '.' || str[j] == ',' ||
                str[j] == '?') && i - 1 >= 0 &&
                str[i - 1] == ' ')
                str = str.substr(0, i - 1) + str[j++] + str.substr(i);
     
            else
                // copy current character at index i
                // and increment both i and j
                str = str.substr(0, i++) + str[j++] + str.substr(i);
     
            // set space flag to false when any
            // non-space character is found
            spaceFound = false;
        }
        // if current character is a space
        else if (str[j++] == ' ') {
            // If space is encountered for the first
            // time after a word, put one space in the
            // output and set space flag to true
            if (!spaceFound) {
                str = str.substr(0, i++) + ' ' + str.substr(i);
                spaceFound = true;
            }
        }
    }
     
    // Remove trailing spaces
    if (i <= 1)
        str = str.substr(0, i);
    else
        str = str.substr(0, i - 1);
     
    return str;
}
 
// Driver Code
let str = " Hello Geeks . Welcome to"
+ " GeeksforGeeks . ";
 
str = removeSpaces(str);
 
console.log(str);


Output:  

Hello Geeks. Welcome to GeeksforGeeks.

Time complexity of above solution is O(n).
Auxiliary Space is O(1) as the conversion is done in-place.

Method  2:
Another solution using predefined functions in Python 3: 

C++




#include <iostream>
#include <string>
 
int main() {
    std::string input_string = "   Hello Geeks  .  Welcome ,    Do you love Geeks , Geeks  ? ";
    std::string output_string;
    bool space_flag = false; // Flag to check if spaces have occurred
 
    for (size_t index = 0; index < input_string.length(); ++index) {
        if (input_string[index] != ' ') {
            if (space_flag) {
                if (input_string[index] == '.' || input_string[index] == '?' || input_string[index] == ',') {
                    // Do nothing
                } else {
                    output_string += ' ';
                }
                space_flag = false;
            }
            output_string += input_string[index];
        } else if (index > 0 && input_string[index - 1] != ' ') {
            space_flag = true;
        }
    }
 
    std::cout << output_string << std::endl;
    return 0;
}


Java




public class Main {
    public static void main(String[] args) {
        String inputString = "   Hello Geeks  .  Welcome ,    Do you love Geeks , Geeks  ? ";
        String outputString = "";
        boolean spaceFlag = false; // Flag to check if spaces have occurred
 
        for (int index = 0; index < inputString.length(); ++index) {
            if (inputString.charAt(index) != ' ') {
                if (spaceFlag) {
                    if (inputString.charAt(index) == '.' || inputString.charAt(index) == '?' || inputString.charAt(index) == ',') {
                        // Do nothing
                    } else {
                        outputString += ' ';
                    }
                    spaceFlag = false;
                }
                outputString += inputString.charAt(index);
            } else if (index > 0 && inputString.charAt(index - 1) != ' ') {
                spaceFlag = true;
            }
        }
 
        System.out.println(outputString);
    }
}


Python3




# Python program to Remove
# extra spaces from a string
input_string = \
    '   Hello Geeks  .  Welcome ,    Do you love Geeks , Geeks  ? '
output_string = []
space_flag = False # Flag to check if spaces have occurred
 
for index in range(len(input_string)):
 
    if input_string[index] != ' ':
        if space_flag == True:
            if (input_string[index] == '.'
                    or input_string[index] == '?'
                    or input_string[index] == ','):
                pass
            else:
                output_string.append(' ')
            space_flag = False
        output_string.append(input_string[index])
    elif input_string[index - 1] != ' ':
        space_flag = True
 
print (''.join(output_string))


C#




using System;
 
class Program
{
    static void Main()
    {
        string inputString = "   Hello Geeks  .  Welcome to GeeksforGeeks ,    Do you love Geeks , Geeks  ? ";
        char[] outputArray = new char[inputString.Length]; // Using char array for efficient string building
        int outputIndex = 0;
        bool spaceFlag = false; // Flag to check if spaces have occurred
 
        for (int index = 0; index < inputString.Length; ++index)
        {
            if (inputString[index] != ' ')
            {
                if (spaceFlag)
                {
                    // Check if the current character is a punctuation mark
                    if (inputString[index] == '.' || inputString[index] == '?' || inputString[index] == ',')
                    {
                        // Do nothing
                    }
                    else
                    {
                        outputArray[outputIndex++] = ' ';
                    }
                    spaceFlag = false;
                }
                outputArray[outputIndex++] = inputString[index];
            }
            else if (index > 0 && inputString[index - 1] != ' ')
            {
                spaceFlag = true;
            }
        }
 
        string outputString = new string(outputArray, 0, outputIndex); // Convert char array to string
 
        Console.WriteLine(outputString);
    }
}


Javascript




let inputString = "   Hello Geeks  .  Welcome ,    Do you love Geeks , Geeks  ? ";
let outputString = "";
let spaceFlag = false; // Flag to check if spaces have occurred
 
for (let index = 0; index < inputString.length; ++index) {
  if (inputString[index] !== ' ') {
    if (spaceFlag) {
      if (inputString[index] === '.' || inputString[index] === '?' || inputString[index] === ',') {
        // Do nothing
      } else {
        outputString += ' ';
      }
      spaceFlag = false;
    }
    outputString += inputString[index];
  } else if (index > 0 && inputString[index - 1] !== ' ') {
    spaceFlag = true;
  }
}
 
console.log(outputString);


Output:  

Hello Geeks. Welcome to GeeksforGeeks. Do you love Geeks, Geeks?

Time complexity of above solution is O(n). 
Auxiliary Space is O(n) as another list had to be created. 

Method 3: (Using built-in function)

C++




#include <iostream>
#include <string>
#include <regex>
 
int main() {
    std::string str = "   Hello Geeks  .  Welcome ,    Do you love Geeks , Geeks  ? ";
     
    // Use regular expression to replace multiple spaces with a single space
    std::regex pattern("\\s+");
    std::string result = std::regex_replace(str, pattern, " ");
     
    // Remove leading and trailing spaces
    size_t firstNonSpace = result.find_first_not_of(" ");
    size_t lastNonSpace = result.find_last_not_of(" ");
     
    if (firstNonSpace != std::string::npos && lastNonSpace != std::string::npos) {
        result = result.substr(firstNonSpace, lastNonSpace - firstNonSpace + 1);
    }
     
    std::cout << result << std::endl;
     
    return 0;
}
 
// code contributed by shinjanpatra


Java




/**
Java Program to remove extra spaces from a string
**/
 
public class GFG {
  public static void main(String args[]) {
    String str = "   Hello Geeks  .  Welcome ,    Do you love Geeks , Geeks  ? ";
    System.out.println(str.replaceAll("\\s+"," ").trim());
  }
}


Python3




# Python program to remove extra spaces from a string
 
# Input string
str = "   Hello Geeks  .  Welcome ,    Do you love Geeks , Geeks  ? "
 
# Removing extra spaces using regex
import re
str = re.sub('\s+', ' ', str).strip()
 
# Printing the final string
print(str)


C#




// C# Program to remove
// extra spaces from a string
using System;
 
class Program {
    static void Main(string[] args)
    {
        string str
            = "   Hello Geeks  .  Welcome ,    Do you love Geeks , Geeks  ? ";
        // Removing extra spaces using regex and print
        Console.WriteLine(
            System.Text.RegularExpressions.Regex.Replace(
                str.Trim(), @"\s+", " "));
    }
}


Javascript




<script>
 
// JavaScript Program to remove
// extra spaces from a string
var str = "   Hello Geeks  .  Welcome ,    Do you love Geeks , Geeks  ? ";
document.write(str.replace("\\s+", " ").trim());
 
// This code is contributed by rdtank
 
</script>


Output: 

Hello Geeks . Welcome , Do you love Geeks , Geeks ?

Time Complexity: O(n), where n is the number of characters in the string. 
Auxiliary Space: O(1), as there are only lowercase letters.

This article is contributed by Aarti_Rathi and Aditya Goel.

 



Last Updated : 03 Dec, 2023
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