Submission #333748

#	Time	Username	Problem	Language	Result	Execution time	Memory
333748		phathnv	Kangaroo (CEOI16_kangaroo)	C++11	100 / 100	18 ms	14188 KiB

kangaroo

#include <bits/stdc++.h>

#define mp make_pair
#define X first
#define Y second
#define taskname "kangaroo"

using namespace std;

typedef long long ll;
typedef pair <int, int> ii;

const int N = 2001;
const int MOD = 1e9 + 7;

int sum(int a, int b){
    a += b;
    a -= (a >= MOD) * MOD;
    return a;
}

int mul(int a, int b){
    return (ll) a * b % MOD;
}

int n, dp[N][N], cs, cf;

void readInput(){
    cin >> n >> cs >> cf;
}

void solve(){
    dp[0][0] = 1;
    int fixed = 0;
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= i; j++)
            if (i == cs || i == cf)
                dp[i][j] = (dp[i - 1][j] + dp[i - 1][j - 1]) % MOD;
            else
                dp[i][j] = sum(mul(dp[i - 1][j + 1], j), mul(dp[i - 1][j - 1], j - fixed));
        fixed += (i == cs || i == cf);
    }
    cout << dp[n][1];
}

int main(){
    if (fopen(taskname".inp", "r")){
        freopen(taskname".inp", "r", stdin);
        freopen(taskname".out", "w", stdout);
    }
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    readInput();
    solve();
    return 0;
}

Compilation message (stderr)

kangaroo.cpp: In function 'int main()':
kangaroo.cpp:48:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   48 |         freopen(taskname".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
kangaroo.cpp:49:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   49 |         freopen(taskname".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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