Custom Functor in std::set - c++

Question

#include <iostream>
#include <set>
#include <algorithm>
using namespace std;
int order[26];
struct lexcmp
{
bool operator()(const string &s1,const string &s2)
{
int i=0;
int j=min(s1.size(),s2.size());
while(1)
{
if(order[s1[i]-'a']<order[s2[i]-'a'])
return true;
if(order[s1[i]-'a']>order[s2[i]-'a'])
return false;
if(i==j-1)
return false;
i++;
}
}
};
int main()
{
string s;
cin>>s;
for(int i=0;i<s.size();i++)
{
order[s[i]-'a']=i;
}
set<string,lexcmp> store;
int m;
cin>>m;
while(m--)
{
string q;
cin>>q;
store.insert(q);
}
for(auto i=store.begin();i!=store.end();i++)
{
cout<<*i<<endl;
}
}
return 0;
}
Problem in making the Custom Functor
The problem is, i have a new order of elements (instead of simple a-z). //Saved in order array
All i want is order the given strings on the based of new order.
for eg: Order is : bacdefghijklmnopqrstuvwxyz
So if the strings are ss , aa , bb
The new ordering will be bb,aa,ss.
The Code is working fine but it is giving me a problem while the strings are like "pas" "p" to be compared.
p should come before pas but it is coming after.
What modifications should i do in the functor?

Answer 1

Here's one approach:
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <algorithm>
#include <numeric>
#include <array>
#include <string>
#include <locale>
struct lexcmp {
lexcmp() { std::iota(order_.begin(), order_.end(), std::int_fast8_t{}); }
explicit lexcmp(std::string const& order) {
assert(order.size() == order_.size());
for (std::size_t i{}; i != order_.size(); ++i) {
char const order_letter = order[i];
assert(std::isalpha(order_letter, std::locale::classic()));
assert(std::islower(order_letter, std::locale::classic()));
order_[i] = order_letter - 'a';
}
auto unique_order_letters = [this]{
auto order = order_;
std::sort(order.begin(), order.end());
return order.end() - std::unique(order.begin(), order.end()) == 0;
};
assert(unique_order_letters());
}
bool operator ()(std::string const& a, std::string const& b) const {
auto const a_len = a.size(), b_len = b.size();
std::size_t i{};
for (auto const len = std::min(a_len, b_len); i != len; ++i) {
if (auto const diff = order_[a[i] - 'a'] - order_[b[i] - 'a']) {
return diff < 0;
}
}
return i == a_len && i != b_len;
}
private:
std::array<std::int_fast8_t, 26> order_;
};
Online Demo