Submission #515764

#	Time	Username	Problem	Language	Result	Execution time	Memory
515764		CraniXort	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	36 ms	31680 KiB

kangaroo

#include <bits/stdc++.h>

#define fin std::cin
#define fout std::cout



int main(){
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(NULL);
    std::cout.tie(NULL);

    int n, start, stop, flag = 0;
    fin >> n >> start >> stop;

    long long mod = 1000000007;
    long long dp[n+2][n+2] = {};

    dp[0][0] = 1;
    for(int i = 1; i <= n; i ++) {
        if(i == start or i == stop)
            flag ++;
        for(int j = 1; j <= i; j ++) {
            if(i == start or i == stop) {
                dp[i][j] = (dp[i-1][j-1] + dp[i-1][j]) % mod;
                continue;
            }

            dp[i][j] = (dp[i-1][j-1] * (j - flag) + dp[i-1][j+1] * j) % mod;
        }
    }

    fout << dp[n][1] << '\n';

    return 0;
}

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