Submission #677510

#	Time	Username	Problem	Language	Result	Execution time	Memory
677510		stevancv	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	31 ms	15948 KiB

kangaroo

#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define sp ' '
#define en '\n'
#define smin(a, b) a = min(a, b)
#define smax(a, b) a = max(a, b)
using namespace std;
const int N = 2e3 + 2;
const int mod = 1e9 + 7;
int dp[N][N];
int Add(int a, int b) {
    a += b;
    if (a >= mod) a -= mod;
    return a;
}
int Mul(int a, int b) {
    ll c = a; c *= b; c %= mod;
    return c;
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n, a, b;
    cin >> n >> a >> b;
    dp[1][1] = 1;
    for (int i = 2; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            if (i == a || i == b) {
                dp[i][j] = Add(dp[i - 1][j - 1], dp[i - 1][j]);
                continue;
            }
            dp[i][j] = Add(dp[i][j], Mul(j, dp[i - 1][j + 1]));
            int k = j - (i > a) - (i > b);
            dp[i][j] = Add(dp[i][j], Mul(k, dp[i - 1][j - 1]));
        }
    }
    cout << dp[n][1] << en;
    return 0;
}

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