Special Substrings.cpp

#include <bits/stdc++.h>

using namespace std;

#define MOD 1000000007
#define ll long long int
#define ld long double
#define pb push_back
#define mkp make_pair
#define pii pair<int, int> 
#define pll pair<long long int, long long int>
#define sci(x) scanf("%d", &x)
#define scl(x) scanf("%lld", &x)
#define fi first
#define sc second
#define eps 1e-9

vector<pair<char, int> > v;
string s;

int main()
{
	ios_base::sync_with_stdio(false);cout.tie(0);cin.tie(0);

	int n, m, i, j, k, x, y, z;
	cin >> s;
	ll ans = 0;
	char c = s[0];
	int freq = 1;
	for (i = 1; s[i]; ++i) {
		if (s[i] != s[i-1]) {
			v.pb(mkp(c, freq));
			c = s[i];
			freq = 0;
		}
		freq++;
	}
	if (freq > 0) v.pb(mkp(c, freq));
	for (i = 0; i < v.size(); ++i) {
		ans += (1ll * v[i].sc * (v[i].sc + 1ll) / 2);
		if ((i+2 < v.size()) && (v[i].fi == v[i+2].fi) && (v[i+1].sc == 1)) {
			ans += min(v[i].sc, v[i+2].sc);
		}
	}
	cout << ans << endl;

	return 0;
}