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QOJ
ID | Problem | Submitter | Result | Time | Memory | Language | File size | Submit time | Judge time |
---|---|---|---|---|---|---|---|---|---|
#235285 | #6637. Perfect Strings | jzh# | WA | 175ms | 161260kb | C++20 | 1.6kb | 2023-11-02 16:55:56 | 2023-11-02 16:55:56 |
Judging History
answer
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MAXN = 10000005;
const ll Ha = 1e9+7;
ll a[MAXN];
int jc[2*MAXN], ijc[2*MAXN];
ll ksm(ll x, ll k) {
ll ret = 1;
for (; k; k>>=1, x=x*x%Ha)
if (k&1) ret = ret*x %Ha;
return ret;
}
ll binom(ll x, ll y) {
return 1ll*ijc[y] * ijc[x-y] %Ha * jc[x] %Ha;
}
ll inv(ll x) {
if (x <= 1) return 1;
return 1ll*ijc[x] * jc[x-1] %Ha;
}
void solve()
{
ll n, c;
ll tmp, tmp1, tmp2, A, B, iA;
scanf("%lld%lld", &n, &c);
if (n == 1) {
puts("1");
return;
}
if (c == 1) {
printf("%lld\n", n);
return;
}
tmp1 = 1ll*2*(c-1) %Ha *(c-2) %Ha;
tmp2 = 1ll*2*c %Ha * (c-1) %Ha;
for (int i=1; i<=n; i++) {
tmp = 1ll*binom(2*i-1, i) * inv(2*i-1) %Ha * 2 %Ha * ksm(c-1, i);
a[i] = 1ll*tmp2 * tmp %Ha;
//a[i] = tmp;
}
a[0] = ((-tmp2 + tmp1)%Ha + Ha) %Ha;
A = (4-4*c%Ha + Ha) %Ha;
B = (1ll*4*c%Ha*c%Ha*(c-1)%Ha);
iA = ksm(A, Ha-2);
for (int i=0; i<=n; i++) {
a[i] = (a[i]%Ha + Ha) %Ha;
tmp = 1ll*a[i] * iA %Ha;
a[i+1] -= 1ll*B * tmp %Ha;
a[i] = tmp;
}
printf("%lld\n", a[n]);
}
int main()
{
int ttt;
scanf("%d", &ttt);
jc[0] = 1;
for (int i=1; i<2*MAXN; i++) jc[i] = 1ll*jc[i-1]*i %Ha;
ijc[2*MAXN-1] = ksm(jc[2*MAXN-1], Ha-2);
for (int i=2*MAXN-2; i>=0; i--) ijc[i] = 1ll*ijc[i+1] * (i+1) %Ha;
while (ttt--) {
solve();
}
return 0;
}
Details
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Test #1:
score: 0
Wrong Answer
time: 175ms
memory: 161260kb
input:
2 3 1 2 2
output:
3 6
result:
wrong answer 1st numbers differ - expected: '1', found: '3'