Submission #648566

#	Time	Username	Problem	Language	Result	Execution time	Memory
648566		BackNoob	Kangaroo (CEOI16_kangaroo)	C++14	0 / 100	1 ms	340 KiB

kangaroo

#include <bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define endl '\n'
#define MASK(i) (1LL << (i))
#define ull unsigned long long
#define ld long double
#define pb push_back
#define all(x) (x).begin() , (x).end()
#define BIT(x , i) ((x >> (i)) & 1)
#define TASK "task"
#define sz(s) (int) (s).size()

using namespace std;
const int mxN = 5e5 + 227;
const int inf = 1e9 + 277;
const int mod = 1e9 + 7;
const ll infll = 1e18 + 7;
const int base = 307;
const int LOG = 20;

template <typename T1, typename T2> bool minimize(T1 &a, T2 b) {
	if (a > b) {a = b; return true;} return false;
}
template <typename T1, typename T2> bool maximize(T1 &a, T2 b) {
	if (a < b) {a = b; return true;} return false;
}

int n;
int sta;
int fin;
int dp[2007][2007];

void add(int &a, int b)
{
    a += b;
    if(a >= mod)
        a -= mod;
}

void solve()
{
    cin >> n >> sta >> fin;

    dp[0][0] = 1;
    for(int i = 0; i < n; i++) {
        for(int j = 0; j <= i; j++) {
            if(dp[i][j] == 0) continue;
            //cout << i << ' ' << j << ' ' << dp[i][j] << endl;
            if(i + 1 == sta) {
                add(dp[i + 1][j + 1], dp[i][j]);
                add(dp[i + 1][j], dp[i][j]);
                continue;
            }
            if(i + 1 == fin) {
                add(dp[i + 1][j + 1], dp[i][j]);
                add(dp[i + 1][j], dp[i][j]);
                continue;
            }
            add(dp[i + 1][j + 1], 1LL * dp[i][j] * (j + 1 - (i > sta) - (i > fin)) % mod);
            if(j > 1) add(dp[i + 1][j - 1], 1LL * dp[i][j] * (j - 1) % mod);
        }
    }
    cout << dp[n][1];
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    //freopen(TASK".inp" , "r" , stdin);
    //freopen(TASK".out" , "w" , stdout);

    int tc = 1;
    //cin >> tc;
    while(tc--) {
    	solve();
    }
    return 0;
}

• Subtask 1: 0 / 6
• Subtask 2: 0 / 30
• Subtask 3: 0 / 15
• Subtask 4: 0 / 49