Submission #56568

#	Time	Username	Problem	Language	Result	Execution time	Memory
56568		Benq	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	62 ms	16296 KiB

kangaroo

#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>

using namespace std;
using namespace __gnu_pbds;
 
typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;

typedef pair<int, int> pi;
typedef pair<ll,ll> pl;
typedef pair<ld,ld> pd;

typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;

template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;

#define FOR(i, a, b) for (int i=a; i<(b); i++)
#define F0R(i, a) for (int i=0; i<(a); i++)
#define FORd(i,a,b) for (int i = (b)-1; i >= a; i--)
#define F0Rd(i,a) for (int i = (a)-1; i >= 0; i--)

#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()

const int MOD = 1000000007;
const ll INF = 1e18;
const int MX = 2005;

int N, cs, ce, dp[MX][MX];

int ad(int a, int b) { return (a+b)%MOD; }
int sub(int a, int b) { return (a-b+MOD)%MOD; }
int mul(int a, int b) { return (ll)a*b%MOD; }

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    cin >> N >> cs >> ce;
    int cnt = 0;
    dp[0][0] = 1;
    FOR(i,1,N+1) {
        FOR(j,1,N+1) {
            if (i == cs || i == ce) {
                dp[i][j] = ad(dp[i][j],dp[i-1][j-1]); // down
                dp[i][j] = ad(dp[i][j],dp[i-1][j]); // up 
            } else {
                dp[i][j] = ad(dp[i][j],mul(dp[i-1][j-1],j-cnt)); // add new 
                dp[i][j] = ad(dp[i][j],mul(dp[i-1][j+1],j)); // delete old
            }
        }
        if (i == cs || i == ce) cnt ++;
    }
    cout << dp[N][1];
}

/* Look for:
* the exact constraints (multiple sets are too slow for n=10^6 :( ) 
* special cases (n=1?)
* overflow (ll vs int?)
* array bounds
*/

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