CF 1894A 学习笔记 思维 题意理解分析

原题

A. Secret Sport

time limit per test

3 seconds

memory limit per test

512 megabytes

input

standard input

output

standard output

Let's consider a game in which two players, A and B, participate. This game is characterized by two positive integers, � and �.

The game consists of sets, and each set consists of plays. In each play, exactly one of the players, either A or B, wins. A set ends exactly when one of the players reaches � wins in the plays of that set. This player is declared the winner of the set. The players play sets until one of them reaches � wins in the sets. After that, the game ends, and this player is declared the winner of the entire game.

You have just watched a game but didn't notice who was declared the winner. You remember that during the game, � plays were played, and you know which player won each play. However, you do not know the values of � and �. Based on the available information, determine who won the entire game — A or B. If there is not enough information to determine the winner, you should also report it.

Input

Each test contains multiple test cases. The first line contains a single integer � (1≤≤104)(1≤�≤104) - the number of test cases. The description of the test cases follows.

The first line of each test case contains an integer � (1≤≤20)(1≤�≤20) - the number of plays played during the game.

The second line of each test case contains a string � of length �, consisting of characters A and B. If =��=A, it means that player A won the �-th play. If =��=B, it means that player B won the �-th play.

It is guaranteed that the given sequence of plays corresponds to at least one valid game scenario, for some values of � and �.

Output

For each test case, output:

• A — if player A is guaranteed to be the winner of the game.
• B — if player B is guaranteed to be the winner of the game.
• ?? — if it is impossible to determine the winner of the game.

Example

input

Copy

7

5

ABBAA

3

BBB

7

BBAAABA

20

AAAAAAAABBBAABBBBBAB

1

A

13

AAAABABBABBAB

7

BBBAAAA

output

Copy

A
B
A
B
A
B
A

Note

In the first test case, the game could have been played with parameters =3�=3, =1�=1. The game consisted of 11 set, in which player A won, as they won the first 33 plays. In this scenario, player A is the winner. The game could also have been played with parameters =1�=1, =3�=3. It can be shown that there are no such � and � values for which player B would be the winner.

In the second test case, player B won all the plays. It can be easily shown that in this case, player B is guaranteed to be the winner of the game.

In the fourth test case, the game could have been played with parameters =3�=3, =3�=3:

• In the first set, 33 plays were played: AAA. Player A is declared the winner of the set.
• In the second set, 33 plays were played: AAA. Player A is declared the winner of the set.
• In the third set, 55 plays were played: AABBB. Player B is declared the winner of the set.
• In the fourth set, 55 plays were played: AABBB. Player B is declared the winner of the set.
• In the fifth set, 44 plays were played: BBAB. Player B is declared the winner of the set.

In total, player B was the first player to win 33 sets. They are declared the winner of the game.

代码

#include
using namespace std;

int main()
{
	int t;
	scanf("%d",&t);
	
	while(t--)
	{
		int n;
		scanf("%d",&n);
		string s;
		cin>>s;
		printf("%c\n",s[n-1]);
	}
	
	return 0;
}

原题链接

传送门https://codeforces.com/contest/1894/problem/A 总结

参考

1.官方题解

2.赛时rank 1代码

思考

1.题目的意思有点难懂，英文要一个一个单词慢慢看，仔细去理解英文句子背后的意思，这个题目的意思是说，A和B两个人进行一场比赛，比赛有多个回合（sets）,每一个回合有多场（plays），一个回合结束的标志是某一个人赢得X场（plays），某一个人赢得Y个回合，整个比赛结束

2.输入一个数字n，表示总共进行了多少场比赛，然后输入一个字符串，表示每一场比赛的胜利者。

3.我们最后需要输出谁是最终的胜利者，A/B/?，问号表示不能确定谁是最终的胜利者。

4.最后一场的胜利者就是最终的胜利者，因为假设最后一场不能决定胜负，就不会进行最后一场比赛，所以说，代码非常简单，输出最后一场的胜利者即可，也就是字符串的最后一个字符