2018.11.01 neither_nor 的随（rand）

任重而道远

AC代码：

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

const int Mod = 1e9 + 7;
int f[1005], tmp[1005], rt[1005];

int read () {
	int x = 0, f = 0; char c = getchar ();
	while (!isdigit (c)) f |= (c == '-'), c = getchar ();
	while (isdigit (c)) x = x * 10 + c - '0', c = getchar ();
	return f ? -x : x;
}

int mpow (int a, int b) {
	int rt = 1;
	for (; b; b >>= 1, a = 1ll * a * a % Mod)
		if (b & 1) rt = 1ll * rt * a % Mod;
	return rt;
}

int main () {
	freopen ("rand.in", "r", stdin);
	freopen ("rand.out", "w", stdout);
	int n = read (), m = read (), p = read ();
	for (int i = 1; i <= n; i++) {int a = read (); f[a]++;}
	int M = m; rt[1] = 1;
	while (M) {
		if (M & 1) {
			memset (tmp, 0, sizeof (tmp));
			for (int i = 1; i < p; i++)	
				for (int j = 1; j < p; j++)
					tmp[i * j % p] = (tmp[i * j % p] + 1ll * rt[i] * f[j] % Mod) % Mod;
			for (int i = 1; i < p; i++) rt[i] = tmp[i];
		}
		M >>= 1;
		memset (tmp, 0, sizeof (tmp));
		for (int i = 1; i < p; i++)
			for (int j = 1; j < p; j++)
				tmp[i * j % p] = (tmp[i * j % p] + 1ll * f[i] * f[j] % Mod) % Mod;
		for (int i = 1; i < p; i++) f[i] = tmp[i];
	}
	int sww = 0;
	for (int i = 1; i < p; i++) sww = (sww + 1ll * rt[i] * i) % Mod;
	sww = 1ll * sww * mpow (mpow (n, m), Mod - 2) % Mod;
	printf ("%d\n", sww);
	return 0;
}