This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define int long long
#define FOR(i, a, b) for ( int i = a ; i <= b ; i++ )
#define FORD(i, a, b) for (int i = b; i >= a; i --)
#define REP(i, n) for (int i = 0; i < n; ++i)
#define REPD(i, n) for (int i = n - 1; i >= 0; --i)
#define pii pair<int , int>
#define Lg(x) 31 - __builtin_clz(x)
#define MASK(i) (1LL << (i))
#define BIT(x, i) (((x) >> (i)) & 1)
constexpr ll LINF = (1ll << 60);
constexpr int INF = (1ll << 30);
constexpr int MAX = 2e3 + 5;
constexpr int Mod = 1e9 + 7;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
void setupIO(){
#define name "Whisper"
//Phu Trong from Nguyen Tat Thanh High School for gifted student
srand(time(NULL));
cin.tie(nullptr)->sync_with_stdio(false); cout.tie(nullptr);
//freopen(name".inp", "r", stdin);
//freopen(name".out", "w", stdout);
cout << fixed << setprecision(10);
}
template <class X, class Y>
bool minimize(X &x, const Y &y){
X eps = 1e-9;
if (x > y + eps) {x = y; return 1;}
return 0;
}
template <class X, class Y>
bool maximize(X &x, const Y &y){
X eps = 1e-9;
if (x + eps < y) {x = y; return 1;}
return 0;
}
int nArr, numNeed;
unordered_map<string, int> cnt;
vector<string> a;
int dp[MAX][MAX];
//xét đến xâu thứ i đã chọn đc k cặp
#define COST(x) (x) * (x - 1) / 2
void add(int&x, int y){
x += y;
if (x >= Mod) x -= Mod;
}
void Whisper(){
cin >> nArr >> numNeed;
a.push_back("");
for (int i = 1; i <= nArr; ++i){
string s; cin >> s;
sort(s.begin(), s.end());
if (!cnt.count(s)) a.push_back(s);
cnt[s]++;
}
nArr = (int)a.size() - 1;
dp[0][0] = 1;
for (int i = 1; i <= nArr; ++i){
int c = cnt[a[i]];
for (int k = 0; k <= numNeed; ++k){
for (int v = 0; COST(v) <= k && v <= c; ++v){
add(dp[i][k], dp[i - 1][k - v]);
}
}
}
cout << dp[nArr][numNeed];
}
signed main(){
setupIO();
int Test = 1;
// cin >> Test;
for ( int i = 1 ; i <= Test ; i++ ){
Whisper();
if (i < Test) cout << '\n';
}
}
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