//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(){
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();
}
}
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
344 KB |
Output is correct |
| 2 |
Incorrect |
1 ms |
460 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
344 KB |
Output is correct |
| 2 |
Incorrect |
1 ms |
460 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
344 KB |
Output is correct |
| 2 |
Incorrect |
1 ms |
460 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
344 KB |
Output is correct |
| 2 |
Incorrect |
1 ms |
460 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
