Submission #1168788

#	Time	Username	Problem	Language	Result	Execution time	Memory
1168788		spycoderyt	Kangaroo (CEOI16_kangaroo)	C++20	0 / 100	0 ms	324 KiB

kangaroo

#include <bits/stdc++.h>
#define int long long 
using namespace std;
const int N = 2005;
int dp[N][N];
const int mod = 1e9+7;
void add(int &a,int b){
    a = (a + b) % mod;
}
int32_t main() {
    int n,st,en,diff=0;
    cin >> n >> st >> en;
    dp[1][1] = 1;
    for(int i = 1;i<=n+1;i++) {
        for(int j = 1;j<=i;j++) {
            if(i == st || i == en) {
                add(dp[i+1][j],dp[i][j]);
                add(dp[i+1][j+1],dp[i][j]);
            } else {
                add(dp[i+1][j+1],dp[i][j] * (j - (i > st) - (i > en) + 1)); // new cmp
                if(j-1>=1)add(dp[i+1][j-1],dp[i][j] * (j-1)); // merge
            }
            // cerr << dp[i][j] << " ";
        }
        // cerr<<'\n';
    }
    cout << dp[n+1][1];
}
/*
no 3 can be increasing 2x or decreasing 2x

want to use the same update so force structure into the problme

*/

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