# Plat Exercise Bug

I’m not sure why my solution doesn’t work for at least N<=50. I get the first two testcases(so I don’t think my dp is wrong hopefully) and WA on 3-5. The only possible reason I could think of is overflow, but there doesn’t seem to be any I think.

My solution is basically find the number of permutations that have i as the max power for that prime. My dp is basically dp[index][last number finished][0/1(if max seen)]=count.

Also, is there a good way to debug these big combo problems since the test data doesn’t seem to help and my code seems to works for small numbers?

``````#include "bits/stdc++.h"

using namespace std;

typedef long long ll;
typedef long double ld;
typedef double db;
typedef string str;

typedef pair<int,int> pi;
typedef pair<pi, int> pii;
typedef pair<ll,ll> pl;
typedef pair<db,db> pd;

typedef vector<int> vi;
typedef vector<bool> vb;
typedef vector<ll> vl;
typedef vector<db> vd;
typedef vector<str> vs;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<pd> vpd;
template<class T> using V = vector<T>;
template<class T, size_t SZ> using AR = array<T,SZ>;

#define mp make_pair
#define f first
#define s second
#define sz(x) (int)(x).size()
#define all(x) begin(x), end(x)
#define rall(x) (x).rbegin(), (x).rend()
#define sor(x) sort(all(x))
#define rsz resize
#define ins insert
#define ft front()
#define bk back()
#define pf push_front
#define pb push_back
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound

#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define For(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define Rof(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)

template<class T> bool ckmin(T& a, const T& b) {
return b < a ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) {
return a < b ? a = b, 1 : 0; }
constexpr int pct(int x) { return __builtin_popcount(x); }
constexpr int bits(int x) { return 31-__builtin_clz(x); } // floor(log2(x))
ll cdiv(ll a, ll b) { return a/b+((a^b)>0&&a%b); } // divide a by b rounded up
ll fdiv(ll a, ll b) { return a/b-((a^b)<0&&a%b); } // divide a by b rounded down
ll half(ll x) { return fdiv(x,2); }

template<class T, class U> T fstTrue(T lo, T hi, U f) {
// note: if (lo+hi)/2 is used instead of half(lo+hi) then this will loop infinitely when lo=hi
hi ++; assert(lo <= hi); // assuming f is increasing
while (lo < hi) { // find first index such that f is true
T mid = half(lo+hi);
f(mid) ? hi = mid : lo = mid+1;
}
return lo;
}
template<class T, class U> T lstTrue(T lo, T hi, U f) {
lo --; assert(lo <= hi); // assuming f is decreasing
while (lo < hi) { // find first index such that f is true
T mid = half(lo+hi+1);
f(mid) ? lo = mid : hi = mid-1;
}
return lo;
}
template<class T> void remDup(vector<T>& v) {
sort(all(v)); v.erase(unique(all(v)),end(v)); }

// INPUT
template<class A> void re(complex<A>& c);
template<class A, class B> void re(pair<A,B>& p);
template<class A> void re(vector<A>& v);
template<class A, size_t SZ> void re(array<A,SZ>& a);

template<class T> void re(T& x) { cin >> x; }
void re(db& d) { str t; re(t); d = stod(t); }
void re(ld& d) { str t; re(t); d = stold(t); }
template<class H, class... T> void re(H& h, T&... t) { re(h); re(t...); }

template<class A> void re(complex<A>& c) { A a,b; re(a,b); c = {a,b}; }
template<class A, class B> void re(pair<A,B>& p) { re(p.f,p.s); }
template<class A> void re(vector<A>& x) { trav(a,x) re(a); }
template<class A, size_t SZ> void re(array<A,SZ>& x) { trav(a,x) re(a); }

// TO_STRING
#define ts to_string
str ts(char c) { return str(1,c); }
str ts(const char* s) { return (str)s; }
str ts(str s) { return s; }
str ts(bool b) {
#ifdef LOCAL
return b ? "true" : "false";
#else
return ts((int)b);
#endif
}
template<class A> str ts(complex<A> c) {
stringstream ss; ss << c; return ss.str(); }
str ts(vector<bool> v) {
str res = "{"; F0R(i,sz(v)) res += char('0'+v[i]);
res += "}"; return res; }
template<size_t SZ> str ts(bitset<SZ> b) {
str res = ""; F0R(i,SZ) res += char('0'+b[i]);
return res; }
template<class A, class B> str ts(pair<A,B> p);
template<class T> str ts(T v) { // containers with begin(), end()
#ifdef LOCAL
bool fst = 1; str res = "{";
for (const auto& x: v) {
if (!fst) res += ", ";
fst = 0; res += ts(x);
}
res += "}"; return res;
#else
bool fst = 1; str res = "";
for (const auto& x: v) {
if (!fst) res += " ";
fst = 0; res += ts(x);
}
return res;

#endif
}
template<class A, class B> str ts(pair<A,B> p) {
#ifdef LOCAL
return "("+ts(p.f)+", "+ts(p.s)+")";
#else
return ts(p.f)+" "+ts(p.s);
#endif
}

// OUTPUT
template<class A> void pr(A x) { cout << ts(x); }
template<class H, class... T> void pr(const H& h, const T&... t) {
pr(h); pr(t...); }
void ps() { pr("\n"); } // print w/ spaces
template<class H, class... T> void ps(const H& h, const T&... t) {
pr(h); if (sizeof...(t)) pr(" "); ps(t...); }

// DEBUG
void DBG() { cerr << "]" << endl; }
template<class H, class... T> void DBG(H h, T... t) {
cerr << ts(h); if (sizeof...(t)) cerr << ", ";
DBG(t...); }
#ifdef LOCAL // compile with -DLOCAL, chk -> fake assert
#define dbg(...) cerr << "Line(" << __LINE__ << ") -> [" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#define chk(...) if (!(__VA_ARGS__)) cerr << "Line(" << __LINE__ << ") -> function(" \
<< __FUNCTION__  << ") -> CHK FAILED: (" << #__VA_ARGS__ << ")" << "\n", exit(0);
#else
#define dbg(...) 0
#define chk(...) 0
#endif

void dbga(int arr[], int n){vi v;For(i,n)v.pb(arr[i]);dbg(v);}
void dbga(ll arr[], int n){vi v;For(i,n)v.pb(arr[i]);dbg(v);}

// FILE I/O
void setIn(str s) { freopen(s.c_str(),"r",stdin); }
void setOut(str s) { freopen(s.c_str(),"w",stdout); }
void unsyncIO() { cin.tie(0)->sync_with_stdio(0); }
void setIO(str s = "exercise") {
unsyncIO();
// cin.exceptions(cin.failbit);
// throws exception when do smth illegal
// ex. try to read letter into int
if (sz(s)) { setIn(s+".in"), setOut(s+".out"); } // for USACO
}
// 576743 29995400689069LL
int MOD = 1e9+7; // 998244353;
const int MX = 50+5;
const ll INF = 1e18;
const ld PI = acos((ld)-1);
const int xd[4] = {1,0,-1,0}, yd[4] = {0,1,0,-1};

template<int SZ> struct Sieve {
bitset<SZ> pri; vi pr;
Sieve() { // cum[i] = # of primes up to i
pri.set(); pri[0] = pri[1] = 0;
for (int i = 4; i < SZ; i += 2) pri[i] = 0;
for (int i = 3; i*i < SZ; i += 2) if (pri[i])
for (int j = i*i; j < SZ; j += i*2) pri[j] = 0;
F0R(i,SZ) if (pri[i]) pr.pb(i);
}
};
Sieve<320000> S;

vi invs, fac, ifac; // make sure to convert to LL before doing any multiplications ...
void genFac(int SZ) {
invs.rsz(SZ), fac.rsz(SZ), ifac.rsz(SZ);
invs[1] = fac[0] = ifac[0] = 1;
FOR(i,2,SZ) invs[i] = MOD-(ll)MOD/i*invs[MOD%i]%MOD;
FOR(i,1,SZ) {
fac[i] = (ll)fac[i-1]*i%MOD;
ifac[i] = (ll)ifac[i-1]*invs[i]%MOD;
}
}

ll comb(int a, int b) {
if (a < b || b < 0) return 0;
return (ll)fac[a]*ifac[b]%MOD*ifac[a-b]%MOD;
}

typedef unsigned long long ul;
ul mul(ul a, ul b, const ul mod = MOD) {
ll ret = a*b-mod*(ul)((ld)a*b/mod);
return ret+((ret<0)-(ret>=(ll)mod))*mod; }
ul modPow(ul a, ul b, const ul mod = MOD) {
if (b == 0) return 1;
ul res = modPow(a,b/2,mod); res = mul(res,res,mod);
return b&1 ? mul(res,a,mod) : res;
}

ll n;
ll cnt[MX], dp[MX][MX][2];
void go(int x, int prim){
For(i,n+1)For(j,n+1)For(k,2)dp[i][j][k]=0LL;
For(i,n+1)dp[0][i][0]=1LL;

FOR(i,1,n+1)FOR(j,1,n+1){
if(__gcd(x*prim, j)==x*prim){
For(k,2)dp[i][j][k]=dp[i][j-1][k];
continue;
}
int w=0;
For(gr,i/j+1){//#of groups
if(gr==1 && __gcd(x,j)==x)w=1;
int space=gr*j;
For(k,2){
ll tmp=dp[i-space][j-1][k];
tmp=mul(tmp,comb(i,space));//choose from
tmp=mul(tmp,modPow(modPow(j,gr),MOD-2));//rotations
tmp=mul(tmp,ifac[gr]);
tmp=mul(tmp,fac[space]);
dp[i][j][w|k]+=tmp;
dp[i][j][w|k]%=MOD;
}
}
}
cnt[x]=dp[n][n][1];
assert(cnt[x]<MOD);
}
// if(dp[i][j][k]>=MOD)dp[i][j][w|k]-=MOD;

void solve(){
re(n,MOD);
genFac(n+5);
FOR(i,2,n+1)if(S.pri[i]){
int tmp=i;
while(tmp<=n){
go(tmp,i);
tmp*=i;
}
}
ll ret=1LL;
FOR(i,2,n+1)if(cnt[i]){
ret=mul(ret,modPow(i,cnt[i]));
dbg(i,cnt[i]);
}
ps(ret);
}

int main() {
setIO();
solve();
// you should actually read the stuff at the bottom
}

/* stuff you should look for
* int overflow, array bounds
* special cases (n=1?)
* do smth instead of nothing and stay organized
* WRITE STUFF DOWN
* DON'T GET STUCK ON ONE APPROACH
*/
``````

The official solution takes `cnt` modulo MOD-1.

1 Like

thats literally so smart