F - 二分+交互 Gym - 101375H

最新推荐文章于 2020-01-13 10:38:41 发布

原创最新推荐文章于 2020-01-13 10:38:41 发布 · 223 阅读

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本文介绍了一种使用二分法解决交互式问题的方法，具体为在限定次数内猜出Renzo购买的糖果数量，范围从1到10^9。通过不断缩小搜索范围，每次猜测中间值并依据反馈调整，最终准确找到目标值。

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F - 二分+交互 Gym - 101375H

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 ≤ 109. 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 format above. After printing a question, you need to flush the output. See examples below for each language:
C: fflush(stdout)

用二分法做，取开头两端，不断取中间值，在靠近的一半中再取中间值，2^50>1e9，所以50次可行。
交互题，不一样的就是平常输入时这里变输出，输出变输入。记得还要用
fflush(stdout)刷新

#include<stdio.h>
int main(){
	int n,l,r,i;char m;
	n=1e9+1;r=n;l=0;
	for(i=0;i<50;i++){
		n=(l+r)/2;
		printf("Q %d\n",n);
		fflush(stdout);
		scanf("%c",&m);getchar();
		if(m=='<') r=n;
		if(m=='>') l=n;
		if(m=='=') break;
	}
	return 0;
}