Interview Question : Trim multiple consecutive spaces from a string

Question

This is an interview question Looking for best optimal solution to trim multiple spaces from a string. This operation should be in-place operation.

input  =          


        

Answer 1

Trimming multiple spaces also means a space should always be followed by a non space character.

int pack = 0;
char str[] = "I    Like    StackOverflow a      lot";
for (int iter = 1; iter < strlen(str); iter++)
{
    if (str[pack] == ' ' && str[iter] == ' ')
        continue;
    str[++pack] = str[iter];
}
str[++pack] = NULL;

Answer 2

This is a very simple implementation of removing extra whitespaces.

#include <iostream>
std::string trimExtraWhiteSpaces(std::string &str);
int main(){
    std::string str = "  Apple    is a     fruit  and I like     it   .  ";
    str = trimExtraWhiteSpaces(str);
    std::cout<<str;
}
std::string trimExtraWhiteSpaces(std::string &str){
    std::string s;
    bool first = true;
    bool space = false;
    std::string::iterator iter;
    for(iter = str.begin(); iter != str.end(); ++iter){
        if(*iter == ' '){
            if(first == false){
                space = true;
            }
        }else{
            if(*iter != ',' && *iter != '.'){
                if(space){
                    s.push_back(' ');
                }
            }
            s.push_back(*iter);
            space = false;
            first = false;
        }
    }
    return s;
}

Answer 3

int j = 0;
int k=0;
char str[] = "I    Like    StackOverflow a      lot"; 
int length = strlen(str);
char str2[38];
for (int i = 0; i < length; i++) 
{ 
    if (str[i] == ' ' && str[i+1] == ' ') 
     continue; 
    str2[j] = str[i];
    j++;
} 

str2[j] =NULL;

cout<<str2;

Answer 4

A c++0x - solution using a lambda instead of a regular function object. Compare to Cubbi's solution.

#include <string>
#include <algorithm>

int main()
{
    std::string str = "I    Like    StackOverflow a      lot";

    str.erase(std::unique(str.begin(), str.end(),
      [](char a, char b) { return a == ' ' && b == ' '; } ), str.end() );  
}

Answer 5

Does using <algorithm> qualify as "algorithmic solution"?

#include <iostream>
#include <string>
#include <algorithm>
#include <iterator>
struct BothAre
{
    char c;
    BothAre(char r) : c(r) {}
    bool operator()(char l, char r) const
    {
            return r == c && l == c;
    }
};
int main()
{
    std::string str = "I    Like    StackOverflow a      lot";
    std::string::iterator i = unique(str.begin(), str.end(), BothAre(' '));
    std::copy(str.begin(), i, std::ostream_iterator<char>(std::cout, ""));
    std::cout << '\n';
}

test run: https://ideone.com/ITqxB

Answer 6

I'd just go with this:

int main(int argc, char* argv[])
{
    char *f, *b, arr[] = "  This        is    a test.                ";
    f = b = arr;

    if (f) do
    {
        while(*f == ' ' && *(f+1) == ' ') f++;
    } while (*b++ = *f++);

    printf("%s", arr);

    return 0;
}