Remove spaces from a given string

27 Jun, 2022
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++
Java
Python
C#
Javascript
// An efficient C++ program to remove all spaces// from a string#include <iostream>using namespace std; // Function to remove all spaces from a given stringvoid 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 functionint main(){    char str[] = "g  eeks   for ge  eeks  ";    removeSpaces(str);    cout << str;    return 0;}
     // An efficient Java program to remove all spaces// from a stringclass GFG{ // Function to remove all spaces// from a given stringstatic 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 codepublic 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
# Python program to Remove spaces from a given string # Function to remove all spaces from a given stringdef 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 Functiondef toString(List):    return ''.join(List) # Driver programstring = "g  eeks  for ge  eeks  "print removeSpaces(string) # This code is contributed by Bhavya Jain
// An efficient C# program to remove all// spaces from a stringusing System; class GFG{ // Function to remove all spaces// from a given stringstatic 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 codepublic 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
<script>       // An efficient JavaScript program to remove all      // spaces from a string             // Function to remove all spaces      // from a given string      function removeSpaces(str) {        // To keep track of non-space        // character count        var count = 0;         // Traverse the given string. If current        // character is not space, then place        // it at index 'count++'        for (var i = 0; i < str.length; i++)          if (str[i] !== " ") str[count++] = str[i];         // here count is        // incremented         return count;      }       // Driver code      var str = "g eeks for ge eeks ".split("");      var i = removeSpaces(str);      document.write(str.join("").substring(0, i));       </script>
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++
Java
Python
C#
Javascript
// CPP program to Remove spaces// from a given string #include <iostream>#include <algorithm>using namespace std; // Function to remove all spaces from a given stringstring removeSpaces(string str){    str.erase(remove(str.begin(), str.end(), ' '), str.end());    return str;} // Driver program to test above functionint main(){    string str = "g eeks for ge eeks ";    str = removeSpaces(str);    cout << str;    return 0;} // This code is contributed by Divyam Madaan
// 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.
# Python program to Remove spaces from a given string  # Function to remove all spaces from a given stringdef removeSpaces(string):    string = string.replace(' ','')    return string     # Driver programstring = "g  eeks  for ge  eeks  "print(removeSpaces(string)) # This code is contributed by Divyam Madaan
// C# program to remove// all spaces from a stringusing 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
<script>// javascript program to remove// all spaces from a string    // Function to remove all    // spaces from a given string     function removeSpace( str)     {        str = str.replace(/\s/g,'')        return str;    }     // Driver Code           var str = "g eeks for ge eeks ";        document.write(removeSpace(str)); // This code contributed by aashish1995</script>
geeksforgeeeks
Another method to solve this problem using predefined STL functions like count() ,remove() ,getline() and resize() is also present. Here is the implementation for the same :
C++
#include <bits/stdc++.h>using namespace std;int main(){    string s = "g e e k s f o r g e e k s";     cout << "string with spaces is " << s << endl;     int l = s.length(); // storing the length of the string     int c        = count(s.begin(), s.end(),                ' '); // counting the number of whitespaces     remove(s.begin(), s.end(),           ' '); // removing all the whitespaces     s.resize(l - c); // resizing the string to l-c     cout << "string without spaces is " << s << endl;     return 0;}
string with spaces is g e e k s f o r g e e k s
string without spaces is geeksforgeeks
Thanks to Souravi Sarkar for suggesting this problem and initial solution. Java | Removing whitespaces using Regex
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