Submission #212362

#	Time	Username	Problem	Language	Result	Execution time	Memory
212362		bash	Asceticism (JOI18_asceticism)	C++17	100 / 100	108 ms	1152 KiB

asceticism

/**
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*/
#include <cstring>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <queue>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cassert>
 
#define F first
#define S second
#define endl '\n'
#define deb(x) cout<<#x<<' '<<x<<endl;
#define pb push_back
 using namespace __gnu_pbds;
using namespace std;

typedef tree<
int,
null_type,
less<int>,
rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;
/*
#ifdef IZI_KATKA
#define int __int64_t
#else
#define int __int64
#endif
*/
const long long MOD = 1e9 + 7;
const long long MAXN = 1e6 + 1;

typedef long long ll;

#define pii pair<int,int>
 
long long readInt() {
    bool minus1 = false;
    long long result = 0;
    char ch;
    ch = getchar();
    while (true) {
        if (ch == '-') break;
        if (ch >= '0' && ch <= '9') break;
        ch = getchar();
    }
    if (ch == '-') minus1 = true; else result = ch-'0';
    while (true) {
        ch = getchar();
        if (ch < '0' || ch > '9') break;
        result = result*10 + (ch - '0');
    }
    if (minus1)
        return -result;
    else
        return result;
}
#define int ll

int f[MAXN];

long long bin_pow(long long base, long long p) {
    if (p == 1) {
        return base;
    }

    if (p % 2 == 0) {
        long long t = bin_pow(base, p / 2);
        return t * t % MOD;
    } else {
        return bin_pow(base, p - 1) * base % MOD;
    }
}

long long inverse_element(long long x) {
    return bin_pow(x, MOD - 2);
}

//(a / b) mod m
long long divide(long long a, long long b) {
    return a * inverse_element(b) % MOD;
}

int cnk(int n, int k) {
	return divide(f[n], (f[n - k] * f[k]) % MOD);
}

int solve(int n, int k) {
	int sum = 0;
	for (int i = 0; i <= k; i++) {
		int res = cnk(n, i) * bin_pow(k - i, n);
		res %= MOD;
		if (i & 1) {
			res = MOD - res;
		}	
		sum += res;
		sum %= MOD;
	}
	return sum;
}

main() {
	#ifdef IZI_KATKA
	assert(freopen("input", "r", stdin));
    assert(freopen("output", "w", stdout));
    #endif
    int n = readInt(), k = readInt();
	f[0] = 1;    
    for (int i = 1; i <= n; i++) {
		f[i] = (f[i - 1] * i) % MOD;    	
    }
	int ans = solve(n, k);
	ans += ((MOD - solve(n, k - 1)) % MOD);
	ans %= MOD;
	cout << ans << endl;
	return 0;
}

Compilation message (stderr)

asceticism.cpp:122:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main() {
      ^

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