Submission #157405

#	Time	Username	Problem	Language	Result	Execution time	Memory
157405		MrPotato	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	33 ms	16120 KiB

kangaroo

#include <bits/stdc++.h>

#define MAXN 2010
#define ll long long

using namespace std;

const int mod = 1e9 + 7;

int dp[MAXN][MAXN];

int add(int x, int y) {

    x += y;
    return (x >= mod) ? x - mod : x;
}

int mul(int x, int y) {

    return (ll)x * y % mod;
}

int main() {

    int n, cs, cf;
    cin >> n >> cs >> cf;
    
    dp[0][0] = 1;
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j <= n; j++) {
            if(i == cs || i == cf)
                dp[i][j] = add(dp[i - 1][j], dp[i - 1][j - 1]);
            else
                dp[i][j] = add(mul(dp[i - 1][j + 1], j), mul(dp[i - 1][j - 1], j - (i > cs) - (i > cf)));
        }
    }
    
    cout << dp[n][1] << endl;
    return 0;
}

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