oj.uz

Submission #51695

# Submission time Handle Problem Language Result Execution time Memory
51695 2018-06-20T04:48:51 Z shoemakerjo Kangaroo (CEOI16_kangaroo) C++14
100 / 100
 96 ms 16772 KB 
#include <bits/stdc++.h>

using namespace std;
const int mod = 1000000007;
#define ll long long
#define maxn 2010

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

int mult(ll a, ll b) {
	return (a*b)%mod;
}

int go(int cur, int groups) {
	if (cur == N+1) {
		if (groups == 1) return 1;
		return 0; //must have 1 group or else we are bad
	}

	if (groups < 0) return 0;
	if (dp[cur][groups] != -1) {
		return dp[cur][groups]; //already processed this value
	}

	//handle cs and cf separately (i think they might be equivalent though)
	//be careful about edges being bound already
	if (cur == cs || cur == cf) {
		//bind me to my correct side (whatever it is)
		int res = 0;
		//option 1 : add me loosely to my edge
		res += go(cur+1, groups+1);
		res %= mod;

		//option 2 : bind me to the guy when you add me on the edge
		if (groups > 0) {
			res += go(cur+1, groups);
		}
		res %= mod;
		return dp[cur][groups] = res;
	}
	else {
		int numedge = 0; //how many edges there are
		if (cur > cs) numedge++;
		if (cur > cf) numedge++; 

		int numopen = groups+1;
		numopen -= numedge; //one less group here

		int res = 0;

		//option 1 : add me loosely (do it in any open spot, will be surrounded by 2 greater than it)
		res += mult(numopen, go(cur+1, groups+1));
		res %= mod;

		//option 2 : bind 2 groups together (will be surrounded by 2 less than it)
		int numbind = numopen;
		numbind -= 2 - numedge;
		if  (groups >= 2) res += mult(numbind, go(cur+1, groups-1));
		res %= mod;

		return dp[cur][groups] = res;

	} //note that binding to just one group is illegal
}

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cin >> N >> cs >> cf;
	for (int i = 0; i < maxn; i++) {
		fill(dp[i], dp[i]+maxn, -1);
	}

	int ans = go(1, 0);

	

	cout << ans << endl;
	cin >> ans;

}
//given N, cs and cf
// 1 <= cs <= N
// calculate number of ways to go cs to cf if you alternate between left and right
// 2 <= N <= 2000

Subtask #1
6.0 / 6.0

# Verdict Execution time Memory Grader output
1 Correct 15 ms 16120 KB Output is correct
2 Correct 14 ms 16120 KB Output is correct

Subtask #2
30.0 / 30.0

# Verdict Execution time Memory Grader output
1 Correct 15 ms 16120 KB Output is correct
2 Correct 14 ms 16120 KB Output is correct
3 Correct 18 ms 16284 KB Output is correct
4 Correct 17 ms 16396 KB Output is correct
5 Correct 15 ms 16396 KB Output is correct
6 Correct 14 ms 16396 KB Output is correct
7 Correct 15 ms 16396 KB Output is correct
8 Correct 15 ms 16396 KB Output is correct
9 Correct 16 ms 16396 KB Output is correct
10 Correct 15 ms 16396 KB Output is correct
11 Correct 14 ms 16396 KB Output is correct

Subtask #3
15.0 / 15.0

# Verdict Execution time Memory Grader output
1 Correct 15 ms 16120 KB Output is correct
2 Correct 14 ms 16120 KB Output is correct
3 Correct 18 ms 16284 KB Output is correct
4 Correct 17 ms 16396 KB Output is correct
5 Correct 15 ms 16396 KB Output is correct
6 Correct 14 ms 16396 KB Output is correct
7 Correct 15 ms 16396 KB Output is correct
8 Correct 15 ms 16396 KB Output is correct
9 Correct 16 ms 16396 KB Output is correct
10 Correct 15 ms 16396 KB Output is correct
11 Correct 14 ms 16396 KB Output is correct
12 Correct 15 ms 16396 KB Output is correct
13 Correct 15 ms 16396 KB Output is correct
14 Correct 14 ms 16396 KB Output is correct
15 Correct 16 ms 16396 KB Output is correct
16 Correct 16 ms 16516 KB Output is correct
17 Correct 15 ms 16552 KB Output is correct
18 Correct 14 ms 16552 KB Output is correct
19 Correct 15 ms 16552 KB Output is correct
20 Correct 16 ms 16656 KB Output is correct

Subtask #4
49.0 / 49.0

# Verdict Execution time Memory Grader output
1 Correct 15 ms 16120 KB Output is correct
2 Correct 14 ms 16120 KB Output is correct
3 Correct 18 ms 16284 KB Output is correct
4 Correct 17 ms 16396 KB Output is correct
5 Correct 15 ms 16396 KB Output is correct
6 Correct 14 ms 16396 KB Output is correct
7 Correct 15 ms 16396 KB Output is correct
8 Correct 15 ms 16396 KB Output is correct
9 Correct 16 ms 16396 KB Output is correct
10 Correct 15 ms 16396 KB Output is correct
11 Correct 14 ms 16396 KB Output is correct
12 Correct 15 ms 16396 KB Output is correct
13 Correct 15 ms 16396 KB Output is correct
14 Correct 14 ms 16396 KB Output is correct
15 Correct 16 ms 16396 KB Output is correct
16 Correct 16 ms 16516 KB Output is correct
17 Correct 15 ms 16552 KB Output is correct
18 Correct 14 ms 16552 KB Output is correct
19 Correct 15 ms 16552 KB Output is correct
20 Correct 16 ms 16656 KB Output is correct
21 Correct 20 ms 16660 KB Output is correct
22 Correct 25 ms 16664 KB Output is correct
23 Correct 24 ms 16668 KB Output is correct
24 Correct 92 ms 16772 KB Output is correct
25 Correct 92 ms 16772 KB Output is correct
26 Correct 79 ms 16772 KB Output is correct
27 Correct 96 ms 16772 KB Output is correct
28 Correct 53 ms 16772 KB Output is correct