2019_GDUT_新生专题I选集 H Gym - 101375H

题目：

Obs: this is an interactive problem. More information is under the
“Interaction” section.

MaratonIME is gathering to start another group practice. This time, Renzo decided to reward the students with candies as they solve problems. Curious as they are, the members of MaratonIME started to guess how many candies did Renzo bring. For each question, Renzo answered if the amount of candies was higher, lower or equal to the number asked.

Breno, noticing that the amount of candies could be very high, decided to limit the number of queries to 50. This way, the practice would start as soon as possible.

Renzo bought at least 1 and no more than 109 candies. Find how many candies were bought by Renzo with no more than 50 questions.

Input For every question asked, read a character. It will be “?>?” if the amount of Renzo’s candies is higher than your guess, “?<?” if the amount of Renzo’s candies is lower than your guess or “?=?” if your guess is equal to the amount of Renzo’s candies.

Output
You must print every query in the format “Q y”, where y is the number guessed, and 1 ≤ y ≤ 10e9. . After printing a question, you need to flush the output. Check the “Interaction” section for examples of how to flush the output.

Interaction To ask Renzo a question, print the query in the formatabove. After printing a question, you need to flush the output. See examples below for each language:

C: fflush(stdout)

C++: cout.flush()

Java: System.out.flush()

Python: sys.stdout.flush()

Pascal: flush(output)

After each query, read a character as described above.

As soon as Renzo answers your question with “=” the program has to terminate. Your answer will be considered correct if you asked no more than 50 questions.

做法：二分，一开始的l为0，r为1e9+1，如果当前的mid小了就r=mid，不然就l=mid，一直到猜对为止。

代码：

#include<cstdio>
#include<iostream>
using namespace std;

int main()
{
	int ans,l,r,t=50;
	char m;
	r=1e9+1;
	l=0;
	while (t--)
	{
		ans=(l+r)/2;
		cout<<"Q "<<ans<<endl;
		cout.flush();
		scanf("%c",&m);
		getchar();
		if(m=='<') r=ans;
		if(m=='>') l=ans;
		if(m=='=') break;
	}
	return 0;	
}