CareerCup

You've asked for "pairs" when depending on the input A and B you may have arbitrary n-tuples. Could you please clarify the problem.

#include "bits/stdc++.h"
#define FOR(i, a, n) for(int i = a; i < n; i++)
#define ft first
#define sd second
#define so(x) cout<<(x)<<"\n";
#define si(x) cin>>x;
#define ll long long
#define fastScan ios_base::sync_with_stdio(0); cin.tie(NULL);
#define mod 1000000007
using namespace std;

int main() {
	int a, b;
	cin>>a>>b;
	bool marked[b+1];
	for(int i = 0; i <= b; i++)
		marked[i] = false;
	string s = "", s1 = "";
	ll res = 0;
	int count = 0;
	for(int i = a; i <= b; i++) {
		if(marked[i])
			continue;
		marked[i] = true;
		stringstream ss;
		ss << i;
		s = ss.str();
		s1 = s+s;
		int size = s.length();
		count = 1;
		for(int j = 1; j < size; j++) {
			string s2 = s1.substr(j, size);
			int x = atoi(s2.c_str());
			if(x >= a && x <= b && !marked[x]){
				count++;
				marked[x] = true;
			}
		}
		res += (count*(count-1))/2;
	}
	cout<<res<<"\n";
}