Submission #1119632

#	Time	Username	Problem	Language	Result	Execution time	Memory
1119632		gdragon	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	31 ms	14168 KiB

kangaroo

#include <bits/stdc++.h>
using namespace std;
#define TASK "long"
#define fi first
#define se second
#define ll long long
#define pb push_back
#define ALL(x) (x).begin(), (x).end()
#define GETBIT(mask, i) ((mask) >> (i) & 1)
#define MASK(i) ((1LL) << (i))
#define SZ(x) ((int)(x).size())
#define mp make_pair
#define CNTBIT(mask) __builtin_popcount(mask)
template<class X, class Y> bool maximize(X &x, Y y){ if (x < y) {x = y; return true;} return false;};
template<class X, class Y> bool minimize(X &x, Y y){ if (x > y) {x = y; return true;} return false;};
typedef pair<int, int> ii;
const int N = 2000 + 5;
const int inf = 1e9 + 7;
const long long INF = (long long)1e18 + 7;
const int mod = 1e9 + 7;
int calPw(int x, int y) {
    int ans = 1;
    while(y) {
        if (y & 1) ans = 1LL * ans * x % mod;
        x = 1LL * x * x % mod;
        y >>= 1;
    }
    return ans;
}
int n, s, t;
int dp[N][N];
void read() {
    cin >> n >> s >> t;
}
void sub1() {
    vector<int> pos;
    for(int i = 1; i <= n; i++) if (i != s && i != t) pos.push_back(i);
    int ans = 0;
    do {
        int pre = s;
        bool ok = 1;
        for(int i = 0; i < SZ(pos); i++) {
            int cur = pos[i];
            int nxt = (i + 1 < SZ(pos) ? pos[i + 1] : t);
            if (cur > pre) ok &= (cur > nxt);
            if (cur < pre) ok &= (cur < nxt);
            pre = pos[i];
        }
        ans += ok;
    }
    while(next_permutation(ALL(pos)));
    cout << ans;
}
void add(int &x, int y) {
    x += y;
    if (x >= mod) x -= mod;
}
void sub(int &x, int y) {
    x -= y;
    if (x < 0) x += mod;
}
int mul(int x, int y) {
    return 1LL * x * y % mod;
}
void solve() {
    if (s == t) {
        cout << 0;
        return;
    }
    if (n <= 8) {
        sub1();
        return;
    }
    dp[1][1] = 1;
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j <= i; j++) {
            if (i == s || i == t) {
                add(dp[i][j], dp[i - 1][j - 1]); // create new component
                add(dp[i][j], dp[i - 1][j]); // combine i to one of 1->jth block, ith just begin or end of block
            }
            else {
                add(dp[i][j], mul(dp[i - 1][j + 1], j)); // connect two components
                add(dp[i][j], mul(dp[i - 1][j - 1], j - (i > s) - (i > t)));
            }
        }
    }
    cout << dp[n][1];
}
signed main() {
    ios_base::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);
    }
    int test = 1;
    // cin >> test;
    while(test--) {
        read();
        solve();
    }
    return 0;
}

// rmq - rmq2d
// hash
// fw - fw2d
// segtree

Compilation message (stderr)

kangaroo.cpp: In function 'int main()':
kangaroo.cpp:92:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   92 |         freopen(TASK".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
kangaroo.cpp:93:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   93 |         freopen(TASK".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 6 / 6
• Subtask 2: 30 / 30
• Subtask 3: 15 / 15
• Subtask 4: 49 / 49