PROBLEM LINK:
Practice
Contest: Division 1
Contest: Division 2
Contest: Division 3
Contest: Division 4
Author: iceknight1093
Tester: sushil2006
Editorialist: iceknight1093
DIFFICULTY:
Medium
PREREQUISITES:
Combinatorics, prefix sums
PROBLEM:
There are N people, initially standing in the order [1, 2, \ldots, N].
Some of them are priority customers.
You will call some of them several times. If x is called,
- If x is a priority customer, x will move to the front of the line.
- If x is not a priority customer, x will move to the front of the line, but then move behind any existing prefix of priority customers.
You’re given the final order of people after some calls have been made.
For each K, answer the following question:
- How many possible subsets of people of size K could have been priority customers?
EXPLANATION:
Recall from the solution to the easy version: the array must look like a prefix of priority customers, then a contiguous segment of non-priority customers, and finally a sorted suffix of people who were never called; who can be either priority or not.
So, we found the last index r such that A_r \lt A_{r-1}, and then for each prefix from 0 to r-1 we added either 2^{N-r} or 2^{N-r+1} to the answer; since either everything \geq r could be freely decided, or everything \gt r could be freely decided.
It turns out to be quite simple to convert this to a solution that computes the answer for each K.
Indeed, let’s analyze what happens when we fix the required subset size K and perform the earlier algorithm.
If the prefix size i is fixed, we need K-i more elements from the suffix.
Depending on how many elements \lt A_r are contained in the prefix, these K-i elements can be freely chosen from either indices \geq r, or indices \gt r.
That is, the contribution to the answer is either \binom{N-r+1}{K-i} or \binom{N-r}{K-i}.
Further, observe that since what determines which term we need is exactly the number of values \lt A_r in the prefix, there will be some prefix of prefixes (and i = r-1 itself) for which we take \binom{N-r+1}{K-i}, and then everything else will be \binom{N-r}{K-i}.
This means \text{ans}[K] will look something like
for some appropriate break-point j.
Finding j is easy enough, we just need to know the largest prefix that’s missing some element \lt A_r.
Once j is known, we need to actually compute the above summation quickly.
Normally, computing “range sums” of binomial coefficients, with a fixed N, is a hard problem.
Here however, observe that everything is either a choice on N-r+1 or N-r elements.
So, we can simply compute two separate arrays: one for coefficients of the form \binom{N-r+1}{i}, and one more for coefficients of the form \binom{N-r}{i}.
Then, for a fixed K we only require a couple of range sums on these arrays, which is easily done in constant time with the help of prefix sums.
TIME COMPLEXITY:
\mathcal{O}(N) per testcase.
CODE:
Editorialist's code (C++)
// #include <bits/allocator.h>
// #pragma GCC optimize("O3,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include "bits/stdc++.h"
using namespace std;
using ll = long long int;
mt19937_64 RNG(chrono::high_resolution_clock::now().time_since_epoch().count());
/**
* Integers modulo p, where p is a prime
* Source: Aeren (modified from tourist?)
* Modmul for 64-bit mod from kactl:ModMulLL
* Works with p < 7.2e18 with x87 80-bit long double, and p < 2^52 ~ 4.5e12 with 64-bit
*/
template<typename T>
struct Z_p{
using Type = typename decay<decltype(T::value)>::type;
static vector<Type> MOD_INV;
constexpr Z_p(): value(){ }
template<typename U> Z_p(const U &x){ value = normalize(x); }
template<typename U> static Type normalize(const U &x){
Type v;
if(-mod() <= x && x < mod()) v = static_cast<Type>(x);
else v = static_cast<Type>(x % mod());
if(v < 0) v += mod();
return v;
}
const Type& operator()() const{ return value; }
template<typename U> explicit operator U() const{ return static_cast<U>(value); }
constexpr static Type mod(){ return T::value; }
Z_p &operator+=(const Z_p &otr){ if((value += otr.value) >= mod()) value -= mod(); return *this; }
Z_p &operator-=(const Z_p &otr){ if((value -= otr.value) < 0) value += mod(); return *this; }
template<typename U> Z_p &operator+=(const U &otr){ return *this += Z_p(otr); }
template<typename U> Z_p &operator-=(const U &otr){ return *this -= Z_p(otr); }
Z_p &operator++(){ return *this += 1; }
Z_p &operator--(){ return *this -= 1; }
Z_p operator++(int){ Z_p result(*this); *this += 1; return result; }
Z_p operator--(int){ Z_p result(*this); *this -= 1; return result; }
Z_p operator-() const{ return Z_p(-value); }
template<typename U = T>
typename enable_if<is_same<typename Z_p<U>::Type, int>::value, Z_p>::type &operator*=(const Z_p& rhs){
#ifdef _WIN32
uint64_t x = static_cast<int64_t>(value) * static_cast<int64_t>(rhs.value);
uint32_t xh = static_cast<uint32_t>(x >> 32), xl = static_cast<uint32_t>(x), d, m;
asm(
"divl %4; \n\t"
: "=a" (d), "=d" (m)
: "d" (xh), "a" (xl), "r" (mod())
);
value = m;
#else
value = normalize(static_cast<int64_t>(value) * static_cast<int64_t>(rhs.value));
#endif
return *this;
}
template<typename U = T>
typename enable_if<is_same<typename Z_p<U>::Type, int64_t>::value, Z_p>::type &operator*=(const Z_p &rhs){
uint64_t ret = static_cast<uint64_t>(value) * static_cast<uint64_t>(rhs.value) - static_cast<uint64_t>(mod()) * static_cast<uint64_t>(1.L / static_cast<uint64_t>(mod()) * static_cast<uint64_t>(value) * static_cast<uint64_t>(rhs.value));
value = normalize(static_cast<int64_t>(ret + static_cast<uint64_t>(mod()) * (ret < 0) - static_cast<uint64_t>(mod()) * (ret >= static_cast<uint64_t>(mod()))));
return *this;
}
template<typename U = T>
typename enable_if<!is_integral<typename Z_p<U>::Type>::value, Z_p>::type &operator*=(const Z_p &rhs){
value = normalize(value * rhs.value);
return *this;
}
template<typename U>
Z_p &operator^=(U e){
if(e < 0) *this = 1 / *this, e = -e;
Z_p res = 1;
for(; e; *this *= *this, e >>= 1) if(e & 1) res *= *this;
return *this = res;
}
template<typename U>
Z_p operator^(U e) const{
return Z_p(*this) ^= e;
}
Z_p &operator/=(const Z_p &otr){
Type a = otr.value, m = mod(), u = 0, v = 1;
if(a < (int)MOD_INV.size()) return *this *= MOD_INV[a];
while(a){
Type t = m / a;
m -= t * a; swap(a, m);
u -= t * v; swap(u, v);
}
assert(m == 1);
return *this *= u;
}
template<typename U> friend const Z_p<U> &abs(const Z_p<U> &v){ return v; }
Type value;
};
template<typename T> bool operator==(const Z_p<T> &lhs, const Z_p<T> &rhs){ return lhs.value == rhs.value; }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> bool operator==(const Z_p<T>& lhs, U rhs){ return lhs == Z_p<T>(rhs); }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> bool operator==(U lhs, const Z_p<T> &rhs){ return Z_p<T>(lhs) == rhs; }
template<typename T> bool operator!=(const Z_p<T> &lhs, const Z_p<T> &rhs){ return !(lhs == rhs); }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> bool operator!=(const Z_p<T> &lhs, U rhs){ return !(lhs == rhs); }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> bool operator!=(U lhs, const Z_p<T> &rhs){ return !(lhs == rhs); }
template<typename T> bool operator<(const Z_p<T> &lhs, const Z_p<T> &rhs){ return lhs.value < rhs.value; }
template<typename T> bool operator>(const Z_p<T> &lhs, const Z_p<T> &rhs){ return lhs.value > rhs.value; }
template<typename T> bool operator<=(const Z_p<T> &lhs, const Z_p<T> &rhs){ return lhs.value <= rhs.value; }
template<typename T> bool operator>=(const Z_p<T> &lhs, const Z_p<T> &rhs){ return lhs.value >= rhs.value; }
template<typename T> Z_p<T> operator+(const Z_p<T> &lhs, const Z_p<T> &rhs){ return Z_p<T>(lhs) += rhs; }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> Z_p<T> operator+(const Z_p<T> &lhs, U rhs){ return Z_p<T>(lhs) += rhs; }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> Z_p<T> operator+(U lhs, const Z_p<T> &rhs){ return Z_p<T>(lhs) += rhs; }
template<typename T> Z_p<T> operator-(const Z_p<T> &lhs, const Z_p<T> &rhs){ return Z_p<T>(lhs) -= rhs; }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> Z_p<T> operator-(const Z_p<T>& lhs, U rhs){ return Z_p<T>(lhs) -= rhs; }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> Z_p<T> operator-(U lhs, const Z_p<T> &rhs){ return Z_p<T>(lhs) -= rhs; }
template<typename T> Z_p<T> operator*(const Z_p<T> &lhs, const Z_p<T> &rhs){ return Z_p<T>(lhs) *= rhs; }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> Z_p<T> operator*(const Z_p<T>& lhs, U rhs){ return Z_p<T>(lhs) *= rhs; }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> Z_p<T> operator*(U lhs, const Z_p<T> &rhs){ return Z_p<T>(lhs) *= rhs; }
template<typename T> Z_p<T> operator/(const Z_p<T> &lhs, const Z_p<T> &rhs) { return Z_p<T>(lhs) /= rhs; }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> Z_p<T> operator/(const Z_p<T>& lhs, U rhs) { return Z_p<T>(lhs) /= rhs; }
template<typename T, typename U, typename enable_if<is_integral<U>::value>::type* = nullptr> Z_p<T> operator/(U lhs, const Z_p<T> &rhs) { return Z_p<T>(lhs) /= rhs; }
template<typename T> istream &operator>>(istream &in, Z_p<T> &number){
typename common_type<typename Z_p<T>::Type, int64_t>::type x;
in >> x;
number.value = Z_p<T>::normalize(x);
return in;
}
template<typename T> ostream &operator<<(ostream &out, const Z_p<T> &number){ return out << number(); }
/*
using ModType = int;
struct VarMod{ static ModType value; };
ModType VarMod::value;
ModType &mod = VarMod::value;
using Zp = Z_p<VarMod>;
*/
// constexpr int mod = 1e9 + 7; // 1000000007
constexpr int mod = (119 << 23) + 1; // 998244353
// constexpr int mod = 1e9 + 9; // 1000000009
using Zp = Z_p<integral_constant<decay<decltype(mod)>::type, mod>>;
template<typename T> vector<typename Z_p<T>::Type> Z_p<T>::MOD_INV;
template<typename T = integral_constant<decay<decltype(mod)>::type, mod>>
void precalc_inverse(int SZ){
auto &inv = Z_p<T>::MOD_INV;
if(inv.empty()) inv.assign(2, 1);
for(; inv.size() <= SZ; ) inv.push_back((mod - 1LL * mod / (int)inv.size() * inv[mod % (int)inv.size()]) % mod);
}
template<typename T>
vector<T> precalc_power(T base, int SZ){
vector<T> res(SZ + 1, 1);
for(auto i = 1; i <= SZ; ++ i) res[i] = res[i - 1] * base;
return res;
}
template<typename T>
vector<T> precalc_factorial(int SZ){
vector<T> res(SZ + 1, 1); res[0] = 1;
for(auto i = 1; i <= SZ; ++ i) res[i] = res[i - 1] * i;
return res;
}
int main()
{
ios::sync_with_stdio(false); cin.tie(0);
const int N = 2e5 + 5;
auto fac = precalc_factorial<Zp>(N);
auto inv = fac;
for (auto &x : inv) x = 1/x;
auto C = [&] (int n, int r) {
if (n < r or r < 0) return Zp(0);
return fac[n] * inv[r] * inv[n-r];
};
int t; cin >> t;
while (t--) {
int n; cin >> n;
vector a(n, 0);
for (int &x : a) cin >> x;
int st = 0;
for (int i = 0; i+1 < n; ++i) {
if (a[i] > a[i+1]) st = i+1;
}
int less = 0, till = -1;
while (less != a[st]-1) {
++till;
less += a[till] < a[st];
}
vector<Zp> pre(n+1);
for (int i = 0; i <= n; ++i) {
pre[i] = C(n-1-st, i);
if (i) pre[i] += pre[i-1];
}
auto prepre = pre;
for (int i = 1; i <= n; ++i)
prepre[i] += prepre[i-1];
vector<Zp> ans(n+1);
for (int k = 0; k <= n; ++k) {
// for prefix of length i, add pre[k-i] to the answer
// can take prefixes of length 0, 1, 2, ..., min(k, st)
// pre[k] + pre[k-1] + pre[k-2] + ... + pre[k-min(k, st)]
ans[k] = prepre[k];
if (k - min(k, st) > 0) ans[k] -= prepre[k - min(k, st) - 1];
// certain prefixes afford fixing st as well
// let these lengths be 0, 1, 2, ..., x
// then, pre[k-1] + pre[k-2] + ... + pre[k-x-1]
if (k and st > 0) {
ans[k] += prepre[k-1];
if (k-till-1 > 0) ans[k] -= prepre[k-till-2];
}
}
for (int i = n; i >= 1; --i)
ans[i] -= ans[i-1];
for (int i = 0; i <= n-1-st; ++i)
ans[st+1+i] += C(n-1-st, i);
for (auto x : ans) cout << x << ' ';
cout << '\n';
}
}