C++ Program to remove spaces from a string

Given a string, remove all spaces from it. For example “g e e k” should be converted to “geek” and ” g e ” should be converted to “ge”. The idea is to traverse the string from left to right and ignore spaces while traversing. We need to keep track of two indexes, one for the current character being red and the other for the current index in the output. 

Implementation:

C++

// C++ program to evaluate a given expression
#include <iostream>
using namespace std;

char *removeSpaces(char *str)
{
    int i = 0, j = 0;
    while (str[i])
    {
        if (str[i] != ' ')
        str[j++] = str[i];
        i++;
    }
    str[j] = '\0';
    return str;
}

// Driver program to test above function
int main()
{
    char str1[] = "gee k ";
    cout << removeSpaces(str1) << endl;

    char str2[] = " g e e k ";
    cout << removeSpaces(str2);
    return 0;
}

Output

geek
geek

Time complexity: O(n) where n is the number of characters in the input string.
Auxiliary Space: O(1)

Approach 2: using in-built function

The main idea in this approach is we will traverse the whole string and will delete the space by using the in-built erase function from C++ STL.

Time complexity will be O(N) where N is the length of the string and the solution will also be the in-place solution.

C++

//C++ program to remove spaces from
//string using in-built function
#include <bits/stdc++.h>
using namespace std;

//function to remove the spaces from string
void removespace(string s)
{
    //traversing the string
    for (int i = 0; i < s.length(); i++)
    {
        if (s[i] == ' ')
        {
            //using in-built function to erase element
            s.erase(s.begin() + i);
            i--;
        }
    }
    cout << s;
}

int main()
{
    string s = "Gee k ";
    cout << "original string is: " <<s<<endl;
    cout << "final updated string: ";
    //function calling
    removespace(s);
    cout<<endl;
    string s1="G e e k";
    cout << "original string is: " <<s1<<endl;
    cout << "final updated string: ";
    //function calling
    removespace(s1);
    return 0;
}
//this code is contributed by machhaliya muhammad

Output

original string is: Gee k 
final updated string: Geek
original string is: G e e k
final updated string: Geek

Auxiliary Space: O(1), for erasing the character in the string it takes constant time.