Submission #1037536

#	Time	Username	Problem	Language	Result	Execution time	Memory
1037536		RiverFlow	Binaria (CCO23_day1problem1)	C++14	14 / 25	211 ms	116816 KiB

Main

#include <bits/stdc++.h>

#define nl "\n"
#define no "NO"
#define yes "YES"
#define fi first
#define se second
#define vec vector
#define task "main"
#define _mp make_pair
#define ii pair<int, int>
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define evoid(val) return void(std::cout << val)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FOD(i, b, a) for(int i = (b); i >= (a); --i)
#define unq(x) sort(all(x)); x.resize(unique(all(x)) - x.begin())

using namespace std;

template<typename U, typename V> bool maxi(U &a, V b) {
    if (a < b) { a = b; return 1; } return 0;
}
template<typename U, typename V> bool mini(U &a, V b) {
    if (a > b) { a = b; return 1; } return 0;
}

const int N = (int)1e6 + 9;
const int mod = (int)1e9 + 7;

void prepare(); void main_code();

int main() {
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    if (fopen(task".inp", "r")) {
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }
    const bool MULTITEST = 0; prepare();
    int num_test = 1; if (MULTITEST) cin >> num_test;
    while (num_test--) { main_code(); }
}

void prepare() {};

vector<int> g[N];
int a[N], id[N];
bool vis[N];

bool dfs(int u) {
    vis[u] = 1;
    for(int v : g[u]) {
        if (id[v] == (id[u] ^ 1)) {
            return 1;
        }
        if (!vis[v]) {
            id[v] = id[u];
            if (dfs(v)) return 1;
        }
    }

    return 0;
}

int Pow(int a, long long b) {
    int res = 1;
    for(; b > 0; b >>= 1, a = 1ll * a * a % mod)
        if (b & 1) res = 1ll * res * a % mod;
    return res;
}
int add(int a, int b) { return a + b < mod ? a + b : a + b - mod; }
int sub(int a, int b) { return a >= b ? a - b : a - b + mod; }
int mul(int a, int b) { return 1LL * a * b % mod; }
void main_code() {
    int n, k; cin >> n >> k;
    for(int i = 1; i <= n; ++i) cin >> a[i + k - 1];
    memset(id, -1, sizeof id);
    for(int i = k + 1; i <= n; ++i) {
        if (abs(a[i] - a[i - 1]) > 1) evoid(0);
        if (a[i - 1] == a[i] - 1) {
            if (id[i - k] == 1) evoid(0);
            id[i - k] = 0, id[i] = 1;
        } else if (a[i - 1] == a[i] + 1) {
            if (id[i - k] == 0) evoid(0);
            id[i - k] = 1, id[i] = 0;
        } else {
            g[i].push_back(i - k);
            g[i - k].push_back(i);
        }
    }
    for(int i = 1; i <= n; ++i) if (!vis[i] and id[i] != -1) {
        if (dfs(i)) evoid(0);
    }
//    FOR(i, 1, n) cout << id[i] << ' ';

    int sum = 0;
    FOR(i, 1, k) {
        if (id[i] != -1) sum += id[i];
    }
    int f = a[k] - sum;
    if (f < 0) evoid(0);
    FOR(i, k + 1, n) {
        if (id[i-k]!=-1)
            sum-=id[i-k];
        if (id[i]!=-1)
            sum+=id[i];
        if (a[i]-sum != f)evoid(0);
    }
    // dem so bit
    int t=0;
    FOR(i, 1, k) if (id[i]==-1)++t;
    // C(f, t)
    // t! / f! * (t-f)!
    vector<int> P(n+1,0);
    P[0]=1;
    FOR(i,1,n)P[i]=1LL*P[i-1]*i%mod;
    if (t<f)evoid(0);
    cout << mul(P[t], Pow(mul(P[f], P[t-f]) , mod-2));
}


/*     Let the river flows naturally     */

Compilation message (stderr)

Main.cpp: In function 'int main()':
Main.cpp:36:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   36 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:37:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   37 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 3 / 3
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 4 / 4
• Subtask 5: 0 / 4
• Subtask 6: 0 / 7