QOJ.ac
QOJ
ID | Problem | Submitter | Result | Time | Memory | Language | File size | Submit time | Judge time |
---|---|---|---|---|---|---|---|---|---|
#283842 | #7677. Easy Diameter Problem | Max_s_xaM | WA | 2ms | 11624kb | C++14 | 6.5kb | 2023-12-15 16:28:10 | 2023-12-15 16:28:10 |
Judging History
answer
#include <iostream>
#include <vector>
typedef long long ll;
typedef double lf;
// #define DEBUG 1
struct IO
{
#define MAXSIZE (1 << 20)
#define isdigit(x) (x >= '0' && x <= '9')
char buf[MAXSIZE], *p1, *p2;
char pbuf[MAXSIZE], *pp;
#if DEBUG
#else
IO() : p1(buf), p2(buf), pp(pbuf) {}
~IO() {fwrite(pbuf, 1, pp - pbuf, stdout);}
#endif
#define gc() (p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, MAXSIZE, stdin), p1 == p2) ? ' ' : *p1++)
#define blank(x) (x == ' ' || x == '\n' || x == '\r' || x == '\t')
template <typename T>
void Read(T &x)
{
#if DEBUG
std::cin >> x;
#else
bool sign = 0; char ch = gc(); x = 0;
for (; !isdigit(ch); ch = gc())
if (ch == '-') sign = 1;
for (; isdigit(ch); ch = gc()) x = x * 10 + (ch ^ 48);
if (sign) x = -x;
#endif
}
void Read(char *s)
{
#if DEBUG
std::cin >> s;
#else
char ch = gc();
for (; blank(ch); ch = gc());
for (; !blank(ch); ch = gc()) *s++ = ch;
*s = 0;
#endif
}
void Read(char &c) {for (c = gc(); blank(c); c = gc());}
void Push(const char &c)
{
#if DEBUG
putchar(c);
#else
if (pp - pbuf == MAXSIZE) fwrite(pbuf, 1, MAXSIZE, stdout), pp = pbuf;
*pp++ = c;
#endif
}
template <typename T>
void Write(T x)
{
if (x < 0) x = -x, Push('-');
static T sta[35];
int top = 0;
do sta[top++] = x % 10, x /= 10; while (x);
while (top) Push(sta[--top] ^ 48);
}
template <typename T>
void Write(T x, char lst) {Write(x), Push(lst);}
} IO;
#define Read(x) IO.Read(x)
#define Write(x, y) IO.Write(x, y)
#define Put(x) IO.Push(x)
using namespace std;
const int MAXN = 310, MAXM = 610, mod = 1e9 + 7;
int n;
vector <int> e[MAXN];
ll fac[MAXM], inv[MAXM];
inline ll C(int n, int m) {return (n < m || m < 0 ? 0 : fac[n] * inv[m] % mod * inv[n - m] % mod);}
inline ll Calc(int n, int m) {return (n == 0 || m < 0 ? 1 : C(n + m, m));}
int ev[MAXN][2], eid[MAXN][MAXN];
int dis[2][MAXN][MAXN], cnt[2][MAXN][MAXN], mx[2][MAXN];
int len, Mid, Midt;
void DFS(int u, int fa, int rt, bool d)
{
cnt[d][rt][dis[d][rt][u]]++;
for (auto v : e[u])
if (v != fa)
{
dis[d][rt][v] = dis[d][rt][u] + 1;
DFS(v, u, rt, d);
}
}
inline void Init()
{
fac[0] = fac[1] = inv[0] = inv[1] = 1;
for (int i = 2; i < MAXM; i++) fac[i] = fac[i - 1] * i % mod, inv[i] = (mod - mod / i) * inv[mod % i] % mod;
for (int i = 2; i < MAXM; i++) inv[i] = inv[i - 1] * inv[i] % mod;
for (int i = 1; i < n; i++)
{
for (int j = 0; j < 2; j++)
DFS(ev[i][j], ev[i][j ^ 1], i, j);
int cur = 1;
for (int j = n; j >= 0; j--)
if (cnt[0][i][j]) {cur += j, mx[0][i] = j; break;}
for (int j = n; j >= 0; j--)
if (cnt[1][i][j]) {cur += j, mx[1][i] = j; break;}
if (len < cur || (len == cur && !Mid))
{
len = cur;
if (cnt[0][i][(len - 1) / 2] && cnt[1][i][len / 2])
Mid = i, Midt = 1;
else if (cnt[1][i][(len - 1) / 2] && cnt[0][i][len / 2])
Mid = i, Midt = 0;
}
}
}
int f[MAXN][2][MAXN << 1][MAXN];
int main()
{
// freopen("cpr.in", "r", stdin);
// freopen("cpr.out", "w", stdout);
#if DEBUG
#else
ios::sync_with_stdio(0), cin.tie(0);
#endif
Read(n);
for (int i = 1, u, v; i < n; i++)
{
Read(u), Read(v);
ev[i][0] = u, ev[i][1] = v;
eid[u][v] = eid[v][u] = i;
e[u].push_back(v), e[v].push_back(u);
}
Init();
// cout << len << " " << Mid << "\n";
// for (int i = 1; i < n; i++)
// {
// for (int j = 1; j <= n; j++) cout << dis[0][i][j] << ' ';
// cout << "\n";
// for (int j = 1; j <= n; j++) cout << dis[1][i][j] << " ";
// cout << "\n\n";
// }
for (int i = 1; i < n; i++)
for (int j = 0; j < 2; j++)
for (int k = 0; k < n - 1; k++)
f[i][j][1][k] = 2;
for (int r = 2; r <= len; r++)
{
for (int i = 1; i < n; i++)
for (int j = 0; j < 2; j++)
{
if (r == len && i != Mid) continue;
int u = ev[i][j], w = ev[i][j ^ 1], Eid, Vid;
if (mx[i][j] < (r >> 1) || (r != len && mx[i][j ^ 1] < (r + 1 >> 1))) continue;
int cntw, cntu;
for (int k = 0; k < n - r; k++)
{
// cout << i << " " << j << " " << r << " " << k << " #:\n";
if (r & 1)
{
cntw = cnt[j ^ 1][i][r - 1 >> 1];
f[i][j][r][k] = (f[i][j][r][k] + (ll)f[i][j][r - 1][k + cntw] * fac[cntw]) % mod;
}
else
{
cntw = cnt[j ^ 1][i][r - 2 >> 1];
for (auto v : e[u]) if (v != w)
{
Eid = eid[v][u], Vid = (ev[Eid][1] == v);
cntu = cnt[j][i][r >> 1] - cnt[Vid][Eid][r - 2 >> 1];
// cout << Eid << " " << Vid << " " << r - 1 << " " << k << " " << cntu << " " << cntw << "\n";
f[i][j][r][k] = (f[i][j][r][k] + (ll)f[Eid][Vid][r - 1][k + cntu + cntw] * fac[cntw] % mod * fac[cntu] % mod * Calc(cntu, k + cntw)) % mod;
// cout << f[i][j][r][k] << "\n";
}
}
cntu = cnt[j][i][r >> 1];
if (!k) f[i][j][r][k] = (f[i][j][r][k] + (ll)f[i][j ^ 1][r - 1][cntu] * fac[cntu]) % mod;
else for (int m = 1; m <= cntu; m++)
f[i][j][r][k] = (f[i][j][r][k] + (ll)f[i][j ^ 1][r - 1][m] * fac[cntu] % mod * Calc(cntu - m, k - 1)) % mod;
}
}
}
// for (int r = 1; r <= len; r++, cout << "\n")
// for (int i = 1; i < n; i++, cout << "\n")
// for (int j = 0; j < 2; j++)
// for (int k = 0; k < n; k++) cout << f[i][j][r][k] << " ";
ll ans = 0;
if (len & 1) ans = f[Mid][0][len][0];
else ans = f[Mid][Midt][len][0];
cout << ans << "\n";
return 0;
}
Details
Tip: Click on the bar to expand more detailed information
Test #1:
score: 100
Accepted
time: 0ms
memory: 9556kb
input:
3 1 2 3 2
output:
4
result:
ok 1 number(s): "4"
Test #2:
score: -100
Wrong Answer
time: 2ms
memory: 11624kb
input:
5 4 1 4 5 1 2 1 3
output:
0
result:
wrong answer 1st numbers differ - expected: '28', found: '0'