Submission #985549

#	Time	Username	Problem	Language	Result	Execution time	Memory
985549		Blistering_Barnacles	Kangaroo (CEOI16_kangaroo)	C++11	0 / 100	2 ms	604 KiB

kangaroo

//Billions of bilious blue blistering barnacles in a thundering typhoon!
//Yesterday is history, tomorrow is a mystery, today is a gift of God, which is why we call it the present.
#include<bits/stdc++.h>
using namespace std;
void solve(){
    freopen("kangaroo.in", "r", stdin);
    freopen("kangaroo.out", "w", stdout);
    const int mod = (int)1e9 + 7;
    auto add = [&](int x, int y) -> int{
        return x + y - (x + y >= mod) * mod;
    };
    auto mul = [&](int x, int y) -> int{
        return (int64_t)x * y % mod;
    };
    int n, s, e;
    cin >> n >> s >> e;
    vector<vector<int>> dp(n + 1, vector<int>(n + 1, 0));
    dp[1][1] = 1;
    for(int i = 2; i <= n; i++){
        for(int j = 1; j <= i; j++){
            if(i == s){
                //either make a new component on the left or stick it to the leftmost component
                dp[i][j] = add(dp[i - 1][j - 1], dp[i - 1][j]);
            }
            else if(i == e){
                //either make a new component on the right or stick it to the rightmost component
                dp[i][j] = add(dp[i - 1][j - 1], dp[i - 1][j]);
            }
            else{
                //either make a new component or merge to components 
                //num is the number of places to make a new component
                int num = j + 1 - (i > s) - (i > e);
                dp[i][j] = add(mul(num, dp[i - 1][j - 1]), mul(j, dp[i - 1][j + 1]));
            }
        }
    }
    cout << dp[n][1] << "\n";
}
int main(){
    ios::sync_with_stdio(0), cin.tie(0);
    int tt = 1;
    //cin >> tt;
    while(tt--){
        solve();
    }
}

Compilation message (stderr)

kangaroo.cpp: In function 'void solve()':
kangaroo.cpp:6:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
    6 |     freopen("kangaroo.in", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
kangaroo.cpp:7:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
    7 |     freopen("kangaroo.out", "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 6
• Subtask 2: 0 / 30
• Subtask 3: 0 / 15
• Subtask 4: 0 / 49