A. Guess a number!（cf）

最新推荐文章于 2020-12-17 22:42:59 发布

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最新推荐文章于 2020-12-17 22:42:59 发布

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本文介绍了一款名为“Guess a number!”的电视节目背后的逻辑。参与者通过提问来猜测主持人所想的整数，问题包括数字的大小比较。文章详细解释了如何根据一系列问题及其答案找出符合条件的数字，若无解则输出'Impossible'。

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A TV show called "Guess a number!" is gathering popularity. The whole Berland, the old and the young, are watching the show.

The rules are simple. The host thinks of an integer y and the participants guess it by asking questions to the host. There are four types of acceptable questions:

Is it true that y is strictly larger than number x?
Is it true that y is strictly smaller than number x?
Is it true that y is larger than or equal to number x?
Is it true that y is smaller than or equal to number x?

On each question the host answers truthfully, "yes" or "no".

Given the sequence of questions and answers, find any integer value of y that meets the criteria of all answers. If there isn't such value, print "Impossible".

Input

The first line of the input contains a single integer n (1 ≤ n ≤ 10000) — the number of questions (and answers). Next n lines each contain one question and one answer to it. The format of each line is like that: "sign x answer", where the sign is:

">" (for the first type queries),
"<" (for the second type queries),
">=" (for the third type queries),
"<=" (for the fourth type queries).

All values of x are integer and meet the inequation - 109 ≤ x ≤ 109. The answer is an English letter "Y" (for "yes") or "N" (for "no").

Consequtive elements in lines are separated by a single space.

Output

Print any of such integers y, that the answers to all the queries are correct. The printed number y must meet the inequation - 2·109 ≤ y ≤ 2·109. If there are many answers, print any of them. If such value doesn't exist, print word "Impossible" (without the quotes).

Sample test(s)

input
4
>= 1 Y
< 3 N
<= -3 N
> 55 N

output
17

input
2
> 100 Y
< -100 Y

output
Impossible
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
#define M 0x3f3f3f3f
int main()
{
    int n;
    cin>>n;
    int p=M,q=-M;
    string s1,s2;
    int num;
    while(n--)
    {
        cin>>s1>>num>>s2;
        if(s1==">="&&s2=="Y")
        {
            if(q<num)
                q=num;
        }
        else if(s1==">"&&s2=="Y")
        {
            if(q<=num)
                q=num+1;
        }
        else if(s1=="<="&&s2=="Y")
        {
            if(p>num)
                p=num;
        }
        else if(s1=="<"&&s2=="Y")
        {
            if(p>=num)
                p=num-1;
        }
        else if(s1==">="&&s2=="N")
        {
            if(p>=num)
                p=num-1;
        }
        else if(s1==">"&&s2=="N")
        {
            if(p>num)
                p=num;
        }
        else if(s1=="<="&&s2=="N")
        {
            if(q<=num)
                q=num+1;
        }
        else if(s1=="<"&&s2=="N")
        {
            if(q<num)
                q=num;
        }
    }
    if(p<q)
        cout<<"Impossible"<<endl;
    else
        cout<<q<<endl;

return 0;
}