C++, sort through array of numbers to find uniqueness - c++

Question

Say I have an array of 4 different numbers.
int numbers[4] = {50234, 50356, 50454, 50934};
How do you make a nested for loop in C++ to sort through these numbers from back to front in order to identify the required amount of digits needed for uniqueness?
From the example you can tell that you'll need 3 digits from the back to make sure no numbers contain similar tails of numbers. 50234, 50934 = 3 digits to have them unique = 502 and 509 respectively.
What would the for loop look like to go through each of these numbers one by one, number by number, and sort out identical numbers to reach an output of 3?
It would go like this:
4
6 - discard this number, it's not identical
4
4
Then:
3
5 - discard this number
3
Then:
2
9 Hurray! No similar numbers anymore, print out 3 being the answer.
I'm stumped and can't figure it out.
Any help would be greatly appreciated, thank you.

Answer 1

Say you start with
#include <unordered_set>
#include <iostream>
#include <vector>
#include <algorithm>
int main() {
const std::vector<int> numbers{50234, 50356, 50454, 50934};
You can transform it into a vector of strings:
std::vector<std::string> string_numbers;
std::for_each(std::begin(numbers), std::end(numbers), [&](int n){ string_numbers.push_back(std::to_string(n)); });
Now we'll check the number of digits required, starting at 1:
size_t digits = 1;
while(true) {
At each iteration, we'll create an unordered_set
std::unordered_set<std::string> partials;
For each number, we'll attempt to place digits digits of it into the set:
for(const auto &s: string_numbers) {
if(s.size() <= digits) {
std::cout << "not unique" << std::endl;
return 0;
}
partials.insert(s.substr(0, digits));
}
If the size of the set is the size of the vector, we're done:
if(partials.size() == numbers.size()) {
std::cout << digits << " required" << std::endl;
return 0;
}
Otherwise, we need to increase the number of digits:
++digits;
}
}
Full code:
#include <unordered_set>
#include <iostream>
#include <vector>
#include <algorithm>
int main() {
const std::vector<int> numbers{50234, 50356, 50454, 50934};
std::vector<std::string> string_numbers;
std::for_each(std::begin(numbers), std::end(numbers), [&](int n){ string_numbers.push_back(std::to_string(n)); });
size_t digits = 1;
while(true) {
std::unordered_set<std::string> partials;
for(const auto &s: string_numbers) {
if(s.size() <= digits) {
std::cout << "not unique" << std::endl;
return 0;
}
partials.insert(s.substr(0, digits));
}
if(partials.size() == numbers.size()) {
std::cout << digits << " required" << std::endl;
return 0;
}
++digits;
}
}

Answer 2

if you want to sort numbers so use one of sort algorithms let's say bubble sort. then check for uniqueness and store the unique values in a new array then print them:
we make our code for understanding and practice but in a real program we use libraries they are too much powerful and quick:
#include <iostream>
using std::cout;
using std::endl;
int main()
{
int numbers[4] = {50234, 50356, 50454, 50934};
// int numbers[4] = {50234, 50356, 50454, 50356};
for(int i(0); i < 4; i++)
{
for(int j(i + 1); j < 4; j++)
{
if(numbers[i] > numbers[j])
{
numbers[i] ^= numbers[j];
numbers[j] ^= numbers[i];
numbers[i] ^= numbers[j];
}
}
}
for(int i = 0; i < 4; i++)
cout << numbers[i] << ", ";
int nUniq = 0;
bool isUniq = true;
for(int i = 0; i < 4; i++)
{
isUniq = true;
for(int j(i + 1); j < 4; j++)
{
if(numbers[i] == numbers[j])
{
isUniq = false;
break;
}
}
if(isUniq)
nUniq++;
}
cout << nUniq << endl;
int* ptrUniq = new int[nUniq];
int k = 0;
for(int i = 0; i < 4; i++)
{
isUniq = true;
for(int j(i + 1); j < 4; j++)
{
if(numbers[i] == numbers[j])
{
isUniq = false;
break;
}
}
if(isUniq)
{
ptrUniq[k] = numbers[i];
k++;
}
}
cout << "\nhere are uniq values:\n\n";
for(int i = 0; i < nUniq; i++)
cout << ptrUniq[i] << ", ";
delete[] ptrUniq;
ptrUniq = NULL;
cout << endl << endl;
return 0;
}