Ositus

input/code.cpp: In function 'll f(int)':
input/code.cpp:18:34: warning: array subscript has type 'char' [-Wchar-subscripts]
  for (j = i; j >= 0 && !b[i][s[j]]; --j)
                                  ^
input/code.cpp:19:12: warning: array subscript has type 'char' [-Wchar-subscripts]
   b[i][s[j]] = 1;
            ^

#include <iostream>

using namespace std;
using ll = long long;

constexpr ll M = 1e9+7;
string s;
int n;
ll t[1001001];
bool b[1001001][200];

ll f(int i)
{
	if (i < 0 || n <= i) return 1;
	if (i == 0) return 1;
	if (t[i]) return t[i];
	int j;
	for (j = i; j >= 0 && !b[i][s[j]]; --j)
		b[i][s[j]] = 1;
	ll p = 0;
	for (; j < i; ++j)
		p = (p + f(j)) % M;
	return t[i] = p;
}

int main()
{
	cin >> s;
	n = s.size();
	cout << f(n-1) << endl;
}

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 1, 2, 3

Verdict: ACCEPTED

Test 3

Group: 1, 2, 3

Verdict: ACCEPTED

Test 4

Group: 1, 2, 3

Verdict: ACCEPTED

Test 5

Group: 2, 3

Verdict: ACCEPTED

Test 6

Group: 3

Verdict: ACCEPTED

Test 7

Group: 3

Verdict: ACCEPTED