Unique Strings Brute Multiplication

#include<bits/stdc++.h>
using namespace std;


#define endl '\n'
#define ff first
#define ss second
#define pb push_back
// #define int long long
#define sz(v) (int)v.size()
#define inf 2147483647
#define llinf 9223372036854775807
#define all(v) v.begin(),v.end()
#define bp(n) __builtin_popcountll(n)
#define f(i,l,r) for(int i=l;i<=r;i++)
#define rf(i,r,l) for(int i=r;i>=l;i--)
#define fast ios_base::sync_with_stdio(false),cin.tie(NULL),cout.tie(NULL)

const int N = 5e3 + 5, mod = 1e9 + 7, bit = 61;



// Be careful about overflow as we are using integer everywhere

template<const int &MOD>
struct _m_int  // This is our new type which will do operations under modulo MOD
{
    int val;   // Value of variable

    _m_int(int64_t v = 0)  // Typecasting into our data type from 64 bit integer
    {
        if (v < 0) v = v % MOD + MOD;
        if (v >= MOD) v %= MOD;
        val = v;
    }

    static int mod_inv(int a, int m = MOD)
    {
        // https://en.wikipedia.org/wiki/Extended_Euclidean_algorithm#Example
        int g = m, r = a, x = 0, y = 1;

        while (r != 0)
        {
            int q = g / r;
            g %= r; swap(g, r);
            x -= q * y; swap(x, y);
        }

        return x < 0 ? x + m : x;
    }

    explicit operator int() const
    {
        return val;
    }

    explicit operator int64_t() const
    {
        return val;
    }

    _m_int& operator += (const _m_int &other)  // Addition
    {
        val -= MOD - other.val;
        if (val < 0) val += MOD;
        return *this;
    }

    _m_int& operator -= (const _m_int &other)  // Subtraction
    {
        val -= other.val;
        if (val < 0) val += MOD;
        return *this;
    }

    static unsigned fast_mod(uint64_t x, unsigned m = MOD) // Mod operation
    {
#if !defined(_WIN32) || defined(_WIN64)
        return x % m;
#endif
        // Optimized mod for Codeforces 32-bit machines.
        // x must be less than 2^32 * m for this to work, so that x / m fits in a 32-bit integer.
        unsigned x_high = x >> 32, x_low = (unsigned) x;
        unsigned quot, rem;
        asm("divl %4\n"
            : "=a" (quot), "=d" (rem)
            : "d" (x_high), "a" (x_low), "r" (m));
        return rem;
    }

    _m_int& operator*=(const _m_int &other)  // Multiplication
    {
        val = fast_mod((uint64_t) val * other.val);
        return *this;
    }

    _m_int& operator/=(const _m_int &other)  // Division
    {
        return *this *= other.inv();
    }

    friend _m_int operator+(const _m_int &a, const _m_int &b) { return _m_int(a) += b; }
    friend _m_int operator-(const _m_int &a, const _m_int &b) { return _m_int(a) -= b; }
    friend _m_int operator*(const _m_int &a, const _m_int &b) { return _m_int(a) *= b; }
    friend _m_int operator/(const _m_int &a, const _m_int &b) { return _m_int(a) /= b; }

    _m_int& operator++()  // Pre-increment
    {
        val = val == MOD - 1 ? 0 : val + 1;
        return *this;
    }

    _m_int& operator--()  // Pre-decrement
    {
        val = val == 0 ? MOD - 1 : val - 1;
        return *this;
    }

    _m_int operator++(int) { _m_int before = *this; ++*this; return before; }  // Post increment
    _m_int operator--(int) { _m_int before = *this; --*this; return before; }  // Post decrement

    _m_int operator-() const  // Change sign
    {
        return val == 0 ? 0 : MOD - val;
    }

    // Boolean operators
    bool operator==(const _m_int &other) const { return val == other.val; }
    bool operator!=(const _m_int &other) const { return val != other.val; }
    bool operator< (const _m_int &other) const { return val <  other.val; }
    bool operator<=(const _m_int &other) const { return val <= other.val; }
    bool operator> (const _m_int &other) const { return val >  other.val; }
    bool operator>=(const _m_int &other) const { return val >= other.val; }

    _m_int inv() const  // Calculating inverse
    {
        return mod_inv(val);
    }

    _m_int pow(int64_t p) const  // Calculating power
    {
        if (p < 0)
            return inv().pow(-p);

        _m_int a = *this, result = 1;

        while (p > 0)
        {
            if (p & 1)
            {
                result *= a;
            }
            a *= a;
            p >>= 1;
        }

        return result;
    }

    friend ostream& operator<<(ostream &os, const _m_int &m)  // Writing output
    {
        return os << m.val;
    }

};

extern const int MOD = 1e9 + 7;
using mod_int = _m_int<MOD>;


mod_int fact[N], ifact[N];


void pre()
{
    fact[0] = 1;
    int i;
    for (i = 1; i < N; i++)
    {
        fact[i] = (fact[i - 1] * i);
    }
    ifact[N - 1] = fact[N - 1].inv();
    for (i = N - 2; i >= 0; i--)
    {
        ifact[i] = (ifact[i + 1] * (i + 1));
    }
}

vector<mod_int> multiply(vector<mod_int> &a, vector<mod_int> &b)
{
    int n = sz(a);
    int m = sz(b);
    vector<mod_int> res(n + m);
    f(i, 0, n - 1)
    {
        f(j, 0, m - 1)
        {
            res[i + j] += a[i] * b[j];
        }
    }
    return res;
}

signed main()
{
    fast;


    pre();
    string s;
    int mp[26] = {0};
    cin >> s;
    for (auto &x : s)
    {
        mp[x - 'a']++;
    }
    vector<mod_int> res{1};
    f(i, 0, 25)
    {
        if (mp[i] == 0)
        {
            continue;
        }
        vector<mod_int> now;
        f(j, 0, mp[i])
        {
            now.pb(ifact[j]);
        }
        res = multiply(res, now);
    }
    int n = sz(s);
    n = min(n, sz(res));
    mod_int ans = 0;
    f(i, 1, n)
    {
        ans += (fact[i] * res[i]);
    }
    cout << ans;
    return 0;
}