# USACO 2019 January Contest, Gold Problem 1. Cow Poetry

http://www.usaco.org/index.php?page=viewproblem2&cpid=897&lang=en

Hello,

I can’t figure out where my mistake is.
I only pass the first test …

Thanks

``````#include <bits/stdc++.h>

using namespace std;

const int MOD = 1e8 + 7;

inline long long fast_exp(long long n, int k) {
long long res = 1;
while (k > 0) {
if (k % 2) {
res *= n;
res %= MOD;
}
n *= n;
n %= MOD;
k /= 2;
}
return res;
}

int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
freopen("poetry.in", "r", stdin);
freopen("poetry.out", "w", stdout);
int n, m, k;
cin >> n >> m >> k;
vector<pair<int, int>> vec(n);
for (auto& i: vec) cin >> i.first >> i.second;
sort(vec.begin(), vec.end());
vector<long long> dp(k + 1);
dp[0] = 1;
for (int i = 1; i <= k; ++i) {
for (int j = 0; j < n && i - vec[j].first >= 0; ++j) {
dp[i] += dp[i - vec[j].first];
dp[i] %= MOD;
}
}
vector<long long> score(n + 1);
for (const auto& i: vec) {
score[i.second] +=  dp[k - i.first];
score[i.second] %= MOD;
}
vector<int> val(26);
while (m--) {
char c;
cin >> c;
++val[c - 'A'];
}
long long ans = 1;
for (int i: val) {
if (!i) continue;
long long cnt = 0;
for (int j: score) {
if (!j) continue;
cnt += fast_exp(j, i);
cnt %= MOD;
}
ans *= cnt;
ans %= MOD;
}
cout << ans;
}
``````

Could you first explain how your solution works?

I found the error, my modulo is wrong, 1e8 + 7 instead of 1e9 + 7 ^^