How to write a function to remove extra spaces in a string?

Question

C++ / C#

The string is represented as a list. The first field of the list item is a string character. The second is a pointer to the next element of the list, or the NULL end of the list. The result list is formed by modifying the original list.
List item:

struct List
{
  char c;
  List *next;
};

Function to remove spaces:

List *delSpaces(List *p)
{
  p = delSpace(p);
  List *head = p;
  while (p)
  {
    p->next = delSpace(p->next);
    p = p->next;
  }
  return head;
}

This function only removes the spaces before the first word, the rest are left untouched. Please find the mistake. Thank you!

Answer 1

Extra spaces are those of which there is more than one in a row?

List *delSpaces(List *p) {
    for(List **a=&p;*a;){
        if((*a)->c==' ' && (*a)->next && (*a)->next->c==' ') *a=(*a)->next;
        else a=&((*a)->next);
    }
    return p;
}

Not checked.

Answer 2

The simplest thing that comes to mind:

List *delSpaces(List *p) {
    while (p && p->c == ' ')
    {
        p = p->next;
    }

    struct L *head = p;
    struct L *prev = p;
    p = p->next;

    while (p) 
    {
        if (p->c == ' ') 
        {
            prev->next = p->next;
        }
        else 
        {
            prev = p;
        }

        p = p->next;
    }

    return head;
}

PS If Cho, then 5 to me for the lab!

Answer 3

I present my implementation.

struct Item {
  Item(): next(NULL), c('\0') {
  }

  char c;
  Item *next;
};

struct List {
  List(const char* in_str) : item(NULL){
    unsigned size = strlen(in_str);

    item = new Item[size];

    for (unsigned i(0); i < size; ++i) {
      item[i].c = in_str[i];
      
      if (i) {
        item[i-1].next = &item[i];
      }
    }
  }

  ~List() {
    delete[] item;
  }

  void remove(char in_) {
    Item* it = item;

    while (it) {
      if (it->c == in_) {
        *it = *it->next;
      }

      if (it->next) {
        if (it->c != in_) {
          it += (it->next - it);
        }
      } else {
        if (it->c == in_) {
          it->c = '\0';
        }
        break;
      }
    }
  }

  const char* takeString() {
    const unsigned size = 255;
    char str[size];

    Item* it = item;
    char* ptrstr = (char*)&str;

    memset(&str, '\0', size);

    while (it) {
      *ptrstr = it->c;

      if (!it->next) {
        break;
      }
          
      if (it->next) {
        it += (it->next - it);
        ++ptrstr;
      } else {
        break;
      }
    }

    return str;
  }

  Item* item;
};

int main()
{
  List list("    bla1         bla2  bla3    ");

  list.remove(' ');

  printf("\n begin[%s%s\n", list.takeString(), "]end");

  return 0;
}