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ID | Problem | Submitter | Result | Time | Memory | Language | File size | Submit time | Judge time |
---|---|---|---|---|---|---|---|---|---|
#320446 | #8211. Enumerating Substrings | ucup-team2303# | WA | 140ms | 34972kb | C++11 | 2.1kb | 2024-02-03 16:56:38 | 2024-02-03 16:56:39 |
Judging History
answer
/*
60 + 0 + 100 + 64 = 224.
*/
#include <bits/stdc++.h>
using namespace std;
#define int long long
//#define int __int128
#define L(i, j, k) for (int i = (j); i <= (k); i++)
#define R(i, j, k) for (int i = (j); i >= (k); i--)
#define pb push_back
#define pii pair<int, int>
inline int read()
{
int sum = 0, nega = 1;
char ch = getchar();
while (ch > '9'||ch < '0')
{
if (ch == '-') nega = -1;
ch = getchar();
}
while (ch <= '9' && ch >= '0') sum = sum * 10 + ch - '0', ch = getchar();
return sum * nega;
}
const int N = 4009, M = 2e6 + 9, mod = 1e9 + 7, inv2 = (mod + 1) / 2;
inline void add(int &x, int y) {x = (x + y) % mod;}
inline void del(int &x, int y) {x = (x - y + mod) % mod;}
inline int Pow(int x, int y)
{
int res = 1, base = x % mod;
while(y)
{
if(y & 1) res = res * base % mod;
base = base * base % mod; y >>= 1;
} return res;
}
int tt[N];
int n, m, k, ans, C[N][N], jc[N], nw, pown[M];
inline int f(int x, int y)
{
if(x == 0 && y == 0) return 1;
if(y <= x / 2) return 0;
if(y <= 0) return 0;
int res = 0;
tt[0] = 1;
L(i, 1, x) tt[i] = tt[i - 1] * (y - i + 1) % mod * Pow(i, mod - 2) % mod;
L(i, 0, x / 2)
{
int tmp = tt[x - i] * C[x - i][i] % mod;
tmp = tmp * jc[x] % mod; tmp = tmp * Pow(inv2, i) % mod;
res = (res + tmp) % mod;
}
return res;
}
signed main()
{
n = read(), m = read(), k = read(); pown[0] = 1;
L(i, 1, n) pown[i] = pown[i - 1] * k % mod;
L(i, 0, m) C[i][i] = C[i][0] = 1;
jc[0] = 1;
L(i, 1, m) jc[i] = jc[i - 1] * i % mod;
L(i, 1, m)
L(j, 1, i - 1) C[i][j] = (C[i - 1][j] + C[i - 1][j - 1]) % mod;
ans = (ans + f(m, k) * Pow(k, n - m) % mod * (n - m + 1) % mod) % mod;
nw = 1;
L(i, 1, m / 2)
{
nw = nw * (k - i + 1) % mod;
int tt = f(m - i * 2, k - i) * nw % mod, sum = 0;
L(j, 2, 1e9)
{
int w = m + (m - i) * (j - 1);
if(w > n) break;
if(j % 2 == 0) sum = (sum - pown[n - w] * (n - w + 1) % mod + mod) % mod;
else sum = (sum + pown[n - w] * (n - w + 1) % mod) % mod;
}
ans = (ans + sum * tt % mod) % mod;
}
ans = (ans % mod + mod) % mod;
cout << ans << endl;
return 0;
}
Details
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Test #1:
score: 100
Accepted
time: 1ms
memory: 5640kb
input:
4 2 3
output:
228
result:
ok 1 number(s): "228"
Test #2:
score: 0
Accepted
time: 140ms
memory: 34972kb
input:
999999 1999 12345678
output:
52352722
result:
ok 1 number(s): "52352722"
Test #3:
score: -100
Wrong Answer
time: 0ms
memory: 5596kb
input:
7 4 2
output:
999999999
result:
wrong answer 1st numbers differ - expected: '182', found: '999999999'