Remove spaces from a given string

Given a string, remove all spaces from the string and return it.

Input:  "g  eeks   for ge  eeks  "
Output: "geeksforgeeks"

Expected time complexity is O(n) and only one traversal of string.



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Below is a Simple Solution

1) Iterate through all characters of given string, do following
   a) If current character is a space, then move all subsequent
      characters one position back and decrease length of the 
      result string.

Time complexity of above solution is O(n2).

A Better Solution can solve it in O(n) time. The idea is to keep track of count of non-space character seen so far.

1) Initialize 'count' = 0 (Count of non-space character seen so far)
2) Iterate through all characters of given string, do following
     a) If current character is non-space, then put this character
        at index 'count' and increment 'count'
3) Finally, put '\0' at index 'count'

Below is the implementation of above algorithm.

C++

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// An efficient C++ program to remove all spaces
// from a string
#include <iostream>
using namespace std;
  
// Function to remove all spaces from a given string
void removeSpaces(char *str)
{
    // To keep track of non-space character count
    int count = 0;
  
    // Traverse the given string. If current character
    // is not space, then place it at index 'count++'
    for (int i = 0; str[i]; i++)
        if (str[i] != ' ')
            str[count++] = str[i]; // here count is
                                   // incremented
    str[count] = '\0';
}
  
// Driver program to test above function
int main()
{
    char str[] = "g  eeks   for ge  eeks  ";
    removeSpaces(str);
    cout << str;
    return 0;
}

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Java

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// An efficient Java program to remove all spaces
// from a string
class GFG
{
  
// Function to remove all spaces 
// from a given string
static int removeSpaces(char []str)
{
    // To keep track of non-space character count
    int count = 0;
  
    // Traverse the given string.
    // If current character
    // is not space, then place 
    // it at index 'count++'
    for (int i = 0; i<str.length; i++)
        if (str[i] != ' ')
            str[count++] = str[i]; // here count is
                                    // incremented
          
    return count;
}
  
// Driver code
public static void main(String[] args)
{
    char str[] = "g eeks for ge eeks ".toCharArray();
    int i = removeSpaces(str);
    System.out.println(String.valueOf(str).subSequence(0, i));
}
  
// This code is contributed by Rajput-Ji

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Python

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# Python program to Remove spaces from a given string
  
# Function to remove all spaces from a given string
def removeSpaces(string):
  
    # To keep track of non-space character count
    count = 0
  
    list = []
  
    # Traverse the given string. If current character
    # is not space, then place it at index 'count++'
    for i in xrange(len(string)):
        if string[i] != ' ':
            list.append(string[i])
  
    return toString(list)
  
# Utility Function
def toString(List):
    return ''.join(List)
  
# Driver program
string = "g  eeks  for ge  eeks  "
print removeSpaces(string)
  
# This code is contributed by Bhavya Jain

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C#

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// An efficient C# program to remove all 
// spaces from a string 
using System;
  
class GFG 
  
// Function to remove all spaces 
// from a given string 
static int removeSpaces(char []str) 
    // To keep track of non-space 
    // character count 
    int count = 0; 
  
    // Traverse the given string. If current
    // character is not space, then place 
    // it at index 'count++' 
    for (int i = 0; i < str.Length; i++) 
        if (str[i] != ' '
            str[count++] = str[i]; // here count is 
                                   // incremented 
  
    return count; 
  
// Driver code 
public static void Main(String[] args) 
    char []str = "g eeks for ge eeks ".ToCharArray(); 
    int i = removeSpaces(str); 
    Console.WriteLine(String.Join("", str).Substring(0, i)); 
  
// This code is contributed by 29AjayKumar

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Output:

geeksforgeeeks

Time complexity of above solution is O(n) and it does only one traversal of string.
Another solution suggested by Divyam Madaan is to use predefined functions. Here is the implementation:

C/C++

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// CPP program to Remove spaces 
// from a given string
   
#include <iostream>
#include <algorithm>
using namespace std;
  
// Function to remove all spaces from a given string
string removeSpaces(string str) 
{
    str.erase(remove(str.begin(), str.end(), ' '), str.end());
    return str;
}
  
// Driver program to test above function
int main() 
{
    string str = "g  eeks   for ge  eeks   ";
    str = removeSpaces(str);
    cout << str;
    return 0;
}
  
// This code is contributed by Divyam Madaan

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Java

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// Java program to remove 
// all spaces from a string
  
class GFG {
      
    // Function to remove all 
    // spaces from a given string
    static String removeSpace(String str)
    {
        str = str.replaceAll("\\s","");
        return str;
    }
  
    // Driver Code
    public static void main(String args[])
    {
        String str = "g eeks for ge eeks ";
        System.out.println(removeSpace(str));
    }
}
  
// This code is contributed by Kanhaiya.

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Python

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# Python program to Remove spaces from a given string
   
# Function to remove all spaces from a given string
def removeSpaces(string):
    string = string.replace(' ','')
    return string
      
# Driver program
string = "g  eeks  for ge  eeks  "
print(removeSpaces(string))
  
# This code is contributed by Divyam Madaan

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C#

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// C# program to remove 
// all spaces from a string 
using System;
  
class GFG 
      
    // Function to remove all 
    // spaces from a given string 
    static String removeSpace(String str) 
    
        str = str.Replace(" ",""); 
        return str; 
    
  
    // Driver Code 
    public static void Main() 
    
        String str = "g eeks for ge eeks "
        Console.WriteLine(removeSpace(str)); 
    
  
// This code is contributed by 
// PrinciRaj1992 

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Output:

geeksforgeeeks

Thanks to Souravi Sarkar for suggesting this problem and initial solution.

Java | Removing whitespaces using Regex

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