Submission #343876

#	Time	Username	Problem	Language	Result	Execution time	Memory
343876		ignaciocanta	Asceticism (JOI18_asceticism)	C++14	100 / 100	33 ms	1280 KiB

asceticism

#include <iostream>
#include <algorithm>
#include <set>
#include <map>
#include <queue>
#include <cmath>
#include <utility>
 
using namespace std;
 
using tint = long long;
using ld = long double;
 
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)
 
using pi = pair<tint,tint>;
using pl = pair<tint,tint>;
using vi = vector<int>;
using vpi = vector<pi>;
using vvi = vector<vi>;
using vl = vector<tint>;
using vb = vector<bool>;

#define pb push_back
#define pf push_front
#define rsz resize
#define all(x) begin(x), end(x)
#define rall(x) x.rbegin(), x.rend() 
#define sz(x) (int)(x).size()
#define ins insert

#define f first
#define s second
#define mp make_pair
 
#define DBG(x) cerr << #x << " = " << x << endl;
 
const int MOD = 1e9+7;
const int mod = 998244353;
const int MX = 1005; 
const tint INF = 1e18; 
const int inf = 2e9;
const ld PI = acos(ld(-1)); 
const ld eps = 1e-8;
 
const int dx[4] = {0, 0, -1, 1};
const int dy[4] = {1, -1, 0, 0};
 
template<class T> void remDup(vector<T> &v){ 
    sort(all(v)); v.erase(unique(all(v)),end(v));
}
 
bool valid(int x, int y, int n, int m){
    return (0<=x && x<n && 0<=y && y<m);
}
 
int cdiv(int a, int b) { return a/b+((a^b)>0&&a%b); } //redondea p arriba
int fdiv(int a, int b) { return a/b-((a^b)<0&&a%b); } //redonde p abajo
 
void NACHO(string name = "lightson"){
    ios_base::sync_with_stdio(0); cin.tie(0);
    //freopen((name+".in").c_str(), "r", stdin);
    //freopen((name+".out").c_str(), "w", stdout);
}

tint fact[100005];

void fill(){
	fact[0] = 1LL;
	FOR(i, 1, 100002){
		fact[i] = (fact[i-1] * i % MOD) % MOD;
	}
}

tint bexp(tint a, tint b){
	a %= MOD;
	tint ret = 1;
	while(b > 0){
		if(b & 1) ret = ret * a % MOD;
		a = a * a % MOD; 
		b >>= 1;
	}
	return ret;
}

tint inv(tint a){
	return bexp(a, MOD-2);
}

tint binom(tint a, tint b){
	tint u = fact[a];
	tint d = (fact[b] * fact[a-b]) % MOD;
	return (u * inv(d)) % MOD;
}

int main(){
	NACHO();
	tint a, b; cin >> a >> b;
	b = a-b;
	fill();
	tint ret = 0;
	F0R(i, b+1){
		ret += (bexp(-1, i) * binom(a+1, i) % MOD * bexp(b + 1 - i, a) % MOD) % MOD;
	}
	cout << ((ret % MOD) + MOD) % MOD<< endl;
}

• Subtask 1: 4 / 4
• Subtask 2: 20 / 20
• Subtask 3: 25 / 25
• Subtask 4: 51 / 51