codeforces 416 A. Guess a number!(简单模拟题)

1、http://codeforces.com/problemset/problem/416/A

2、题目：

A. Guess a number!

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

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

3、AC代码：

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
#define INF 2*1000000000
int main()
{
    int n,x;
    char str[5];
    char ch;
    int a;
    int b;
    while(scanf("%d",&n)!=EOF)
    {
        a=-INF;
        b=INF;
        int flaga=0,flagb=0;//0表示开区间
        while(n--)
        {
            scanf("%s%d",str,&x);
            getchar();
            scanf("%c",&ch);
            int l=strlen(str);
            //printf("%s %d %c\n",str,x,ch);
            if(l==1)
            {
                if(str[0]=='>')
                {
                    if(ch=='Y' && x>=a)
                    {
                        a=x;
                        flaga=0;
                    }
                    else if(ch=='N' && x<b)
                    {
                        b=x;
                        flagb=1;
                    }
                }
                else if(str[0]=='<')
                {
                    if(ch=='Y' && x<=b)
                    {
                        b=x;
                        flagb=0;
                    }
                    else if(ch=='N' && x>a)
                    {
                        a=x;
                        flaga=1;
                    }
                }
            }
            else if(l==2)
            {
                if(str[0]=='>')
                {
                    if(ch=='Y' && x>a)
                    {
                        //printf("a=%d\n",a);
                        a=x;
                        flaga=1;
                    }
                    else if(ch=='N' && x<=b)
                    {
                        b=x;
                        flagb=0;
                    }
                }
                else if(str[0]=='<')
                {
                    if(ch=='Y' && x<b)
                    {
                        b=x;
                        flagb=1;
                    }
                    else if(ch=='N' && x>=a)
                    {
                        a=x;
                        flaga=0;
                    }
                }
            }
        }
        if(flaga==1 && flagb==1 && b>=a)
        printf("%d\n",a);
        else if(flaga==1 && flagb==0 && b>a)
        {
            printf("%d\n",a);
        }
        else if(flaga==0 && flagb==1 && a<b)
        {
            printf("%d\n",b);
        }
        else if(flaga==0 && flagb==0)
        {

            if(a!=-INF && b>=a+2)
            {
                printf("%d\n",a+1);
            }
            else if(b!=INF && b>=a+2)
            {

                printf("%d\n",b-1);
            }
             else
            printf("Impossible\n");
        }
        else
        {
            printf("Impossible\n");
        }
    }
    return 0;
}
/*
1
< 1000000000 Y
*/
/*
4
>= 1 Y
< 3 N
<= -3 N
> 55 N
2
> 100 Y
< -100 Y
1
>= 3 Y
1
>= 3 N
1
> 3 N
1
> 3 Y
1
< 3 Y
1
< 3 N
1
<= 3 N
1
<= 3 Y
*/