C/C++ Why aren't insert, erase, and find working in my script?

[member 428835]

Hi all, I'm trying to write a small script to count the largest number of non-repeating strings in a vector. Below is what I wrote, but insert, erase, and find aren't working. Any ideas why?

If the script isn't correct, you don't have to correct it. I'm just wondering why those three commands don't work.

#include <iostream>
#include <unordered_set>
int long_sub(std::string s) {
    int count = 0, L = 0;
    std::unordered_set<std::string> used_str;
    int max_count = 0;
    for(int R = 0; R < s.length(); R++) {
        if(used_str.find(s[R]) != used_str.end()) {    // IF s[R] IS IN used_str  
            used_str.erase(s[L]);
            L += 1;
            count -= 1;
        } else { // IF s[R] IS NOT IN used_str
            used_str.insert(s[R]);
            R += 1;
            count += 1;
        }
        max_count = std::max(max_count, count);
    return count;
    }
}
int main()
{
    std::string s = "abcabcbb";
    auto sol = long_sub(s);
    std::cout << sol;
}

 

[pbuk]

If the script isn't correct, you don't have to correct it. I'm just wondering why those three commands don't work.

Mainly because you have not set any value to used_str, but also erase is not working because the R'th character of a string is not an iterator pointing to an element of an unordered_set.

Anyway how do you know these "commands aren't working"? Is there an error message?

 

[member 428835]

Mainly because you have not set any value to used_str, but also erase is not working because the R'th character of a string is not an iterator pointing to an element of an unordered_set.

Anyway how do you know these "commands aren't working"? Is there an error message?

Can you elaborate on setting a value to used_str? I tried changing the code to something like this for what you said regarding the iterator, but perhaps I'm misunderstanding:

#include <iostream>
#include <unordered_set>
#include <algorithm>
#include <typeinfo>
int long_sub(std::string s) {
    int count = 0, L = 0;
    std::unordered_set<std::string> used_str;
    int max_count = 0;
    auto L = s.begin();
    for(auto R = s.begin(); R != s.end(); R++) {
        if(used_str.find(*R) != used_str.end()) {    // IF s[R] IS IN used_str  
            used_str.erase(*L);
            L++;
            count -= 1;
        } else { // IF s[R] IS NOT IN used_str
            used_str.insert(*R);
            R++;
            count++;
        }
        max_count = std::max(max_count, count);
    return count;
    }
}
int main()
{
    std::string s = {"abcabcbb"};
    auto sol = long_sub(s);
    std::cout << sol;
}

 

[pbuk]

Can you elaborate on setting a value to used_str?

    // Instead of...
    std::unordered_set<std::string> used_str;
    // ...you need:
    std::unordered_set<std::string> used_str = {};

 

[member 428835]

    // Instead of...
    std::unordered_set<std::string> used_str;
    // ...you need:
    std::unordered_set<std::string> used_str = {};

I tried that before too, but still getting the error "no matching member function for call to 'insert'". Any idea? I've googled it but can't find the error

 

[willem2]

I tried that before too, but still getting the error "no matching member function for call to 'insert'". Any idea? I've googled it but can't find the error

insert expects an argument of type std::string, *R is a char.
Don't you want to find substrings of your input string?

 

[pbuk]

"no matching member function for call to 'insert'"

means that you are passing an argument of the wrong type to 'insert'. If you create your unordered set with std::unordered_set<std::string> used_str = {} then you need to pass a <std::string> to insert, not an iterator over a <std::string> as you are trying to do in #5 or a single character as you are trying to do in #1.

I think you are trying to run in CPP before you can walk: you need to go back to the basics before you attempt something like this.

And why are you doing this in CPP anyway, Python is a much easier language to work with structures like strings and lists?

 

[Passerby]

    // Instead of...
    std::unordered_set<std::string> used_str;
    // ...you need:
    std::unordered_set<std::string> used_str = {};

These lines have the same effect. There is no need to "assign a value" to used_str. It is default-constructed.

 

[pbuk]

These lines have the same effect. There is no need to "assign a value" to used_str. It is default-constructed.

Oh how I hate C++ and its "if there are ten different ways of doing something implement them all" design outcome.

 

[member 428835]

Oh how I hate C++ and its "if there are ten different ways of doing something implement them all" design outcome.

Yea but it's fast. Real fast.

 

[member 428835]

Also, got it, thanks!

#include <iostream>
#include <unordered_map>
#include <string>
class Solution {
public:
    int lenLonStr(std::string s) 
    {
        int max_len = 0;
        int L = 0;
        int R = 0;
        int n = s.length();
        std::unordered_map<char, int> char_map;
        while (R < n)
        {
            char c = s[R];
            std::unordered_map<char, int>::iterator it = char_map.find(c);
            if (it == char_map.end())
            {
                char_map[c] = R;
                R++;
                if (char_map.size() > max_len)
                    max_len = char_map.size();
            }
            else
            {
                L = it->second + 1;
                char_map.clear();
                R = L;
            }
        }
        return max_len;
    }
};
int main()
{
    std::string s = "abcshabcbb";
    Solution ob1;
    auto sol = ob1.lenLonStr(s);
    std::cout << sol <<"\n";
    Solution* ptr = &ob1;
    int a = ptr->lenLonStr(s);
    std::cout << a <<"\n";
    std::shared_ptr<Solution> ptr2 = std::make_shared<Solution>();
    int b = ptr2->lenLonStr(s);
    std::cout << b;
}