string, C++ (gcc) - rextester

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#include<iostream>
#include<string>
#include<algorithm>
#include<unordered_set>
#include<vector>

using namespace std;

bool isPalindrome(const string& s)
{
    int i, j;
    for(i=0, j=s.size()-1; i<j; ++i, --j)
    {
        if(s[i]!=s[j])
            break;
    }   
    
    if(i<j)
        return false;
    else 
        return true;
}

void removeDupER(string& s)
{
    for(string::iterator it = s.begin(); it!=s.end(); it++)
    {
        char c = *it;
        s.erase(remove(it+1, s.end(), c), s.end());
    }
}

string removeDupSTL(string& s)
{
    unordered_set<char> se;
    string str;
    
    for(auto& c : s)
    {
        if(se.find(c)==se.end())
        {
            se.insert(c);
            str.push_back(c);
        }
    }
    return str;
}

void removeDupInplace(string& s)
{
    sort(s.begin(), s.end());
    
    int i=0,j=0;
      
    while(i<s.size())
    {
        int j = i+1;
        
        while(j<s.size() && s[i]==s[j])
        {
            s[j]='$';
            j++;
        }
        
        i=j;
    }
    
    cout << s << endl;
    
    i = 0;
    j = 1;
    
    while(j<s.size())
    {
        while(j<s.size() && s[j]=='$')
            j++;
        
        if(j<s.size())
        {
            i++;
            s[i] = s[j];
            j++;
        }
    }
    
    s.resize(i+1);
    
}

int main()
{

string s("ahgfndgcsaaa");
    string t = s;
    cout << s << endl << endl;
    
    cout << "Checking if palindrome.." << isPalindrome(s) << endl;
   
    cout << "Removing duplicates from string using erase_remove...";
    removeDupER(s);
    cout << s << endl;
    
    s = t;
    cout << "Removing duplicates from string using STL containers...";
    s = removeDupSTL(s);
    cout << s << endl;
    
    s = t;
    cout << "Removing duplicates from string in-place using sorting...";
    removeDupInplace(s);
    cout << s << endl;
    
    s = t;
    sort(s.begin(), s.end());
    cout << "After sorting..." << s << endl;
       
    /*   
    cout << "Remove duplicates from sorted string non-STL...";
    removeDup(s);
    cout << s << endl;
    */

}

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Compilation time: 1.13 sec, absolute running time: 0.16 sec, cpu time: 0.09 sec, memory peak: 3 Mb, absolute service time: 1,29 sec