Submission #376623

#	Time	Username	Problem	Language	Result	Execution time	Memory
376623		thiago4532	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	61 ms	32128 KiB

kangaroo

#include <bits/stdc++.h>
#define int int64_t

using namespace std;
const int maxn = 2010;
const int mod = 1e9 + 7;
int dp[maxn][maxn];
int n;
int ini, fim;

int solve(int i, int k) {
    if (i > n && k == 1) return 1;
    else if (i > n) return 0;
    if (dp[i][k] != -1) return dp[i][k];

    int caso1 = solve(i+1, k+1);
    int caso2 = (k ? (i == ini || i == fim ? solve(i+1, k) : solve(i+1, k-1)) : 0);

    if (i == ini || i == fim) return dp[i][k] = (caso1 + caso2)%mod;
    else if (i < ini && i < fim) return dp[i][k] = ( caso1*(k+1) + caso2*(k-1) )%mod;
    else if (i < ini || i < fim) return dp[i][k] = ( caso1*k + caso2*(k-1) )%mod;
    return dp[i][k] = ((k-1)*( caso1 + caso2 ))%mod;
}

int32_t main() {
    memset(dp, -1, sizeof dp);
    cin >> n;
    cin >> ini >> fim;
    cout << solve(1, 0) << '\n';
    return 0;
}

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