Submission #597888

#	Time	Username	Problem	Language	Result	Execution time	Memory
597888		1bin	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	14 ms	23004 KiB

kangaroo

#include <bits/stdc++.h>

using namespace std;

#define all(v) v.begin(), v.end()
typedef long long ll;
const int NMAX = 2e3 + 5;
const ll mod = 1e9 + 7;
ll n, s, f, dp[NMAX][NMAX], chk;

int main(void){
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    
    cin >> n >> s >> f;
    dp[0][0] = 1;
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= i; j++){
            if(i == s || i == f) dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j];
            else dp[i][j] = dp[i - 1][j - 1] * (j - chk) + dp[i - 1][j + 1] * j;
            dp[i][j] %= mod;
        }
        if(i == s || i == f) chk++;
    }
    cout << dp[n][1];
    return 0;
}

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