[training Day12] x equation [high precision] [mathematics]

Ideas ：

We calculate directly g（x）, Then I found that it was a combination of Mathematics
Remember to be highly refined

$code$

#include<iostream>
#include<cstdio>

#define ll long long

using namespace std;

ll n, k;
ll a[10001];

ll qpow(ll x, ll k, ll mod) {
    
	ll ans = 1;
	for(; k; k >>= 1, x = x * x % mod) if(k & 1) ans = ans * x % mod;
	return ans;
}

void cheng(ll x) {
    
	ll g = 0;
	for(ll i = 10000; i >= 1; i --) {
    
		a[i] = a[i] * x + g;
		g = a[i] / 10;
		a[i] %= 10;
	}
}

void chu(ll x) {
    
	ll g = 0;
	for(ll i = 1; i <= 10000; i ++) {
    
		ll p = (g * 10 + a[i]) % x;
		a[i] = (g * 10 + a[i]) / x;
		g = p;
	}
}

// n! / m!(n-m)!
void C(ll n, ll m) {
    
	a[10000] = 1;
	for(ll i = m + 1; i <= n; i ++) cheng(i);
	for(ll i = 2; i <= n - m; i ++) chu(i);
}

void write_() {
    
	ll i = 1;
	while(a[i] == 0 && i + 1 <= 10000) i ++;
	while(i <= 10000) printf("%lld", a[i]), i ++;
}

int main() {
    
	scanf("%lld%lld", &k, &n);
	ll m = qpow(n, n, 1000);
	C(m - 1, k - 1);
	write_();
	return 0;
}