2063. Black and White
Time limit: 1.0 second
Memory limit: 64 MB
Let’s play a game. You are given a row of n balls, each ball is either black or white. Their positions in a row are numbered from 1 to n. You know the total number of balls n, but have no information about the order of their colors. You don’t even know how many white balls are there.
You are allowed to make queries v u (1 ≤ v, u ≤ n). If the ball on position v is black and the ball on position u is white, then these two balls are swapped. Otherwise, nothing happens. Even if the balls are swapped, you don’t get any feedback.
After a number of queries (can be zero) you a required to make a "statement." "Statement" also consists of two positions v, u. Your goal is to choose positions, that contain two balls of the same color.
In this problem we ask you to print both queries and a "statement", that comes after them.
A single test can contain several games. Furthermore, all tests except the first one contain 99 game descriptions. In the first game n = 2, in the second — n = 3 ... in the last game n = 100.
First test is the same as the sample below.
In all other tests your program must make the right statement at least in 80 games.
Note, that we do not guarantee that the tests are random.
Input
First line contains m — number of games in the test. For every test, except for the first one,m=99.
Remaining lines contain ciphered (except for the first test) order of balls in the row. Thus we guarantee, that the tests are determined beforehand and do not depend on your strategy. Please, do not try to use this data in any way and do not try to decipher it.
Output
Output m game descriptions.
One description consists of (k+1) lines, where k — number of queries made by your program.
First k lines should contain the queries in the following format: ? v u (1 ≤ v, u ≤ n, v ≠ u).
The last line should contain the "statement": ! v u (1 ≤ v, u ≤ n, v ≠ u).
Total amount of lines (over all games in a test) should not exceed 5 · 105.
Sample
| input | output |
|---|---|
2 01 101 |
? 1 2 ? 2 1 ? 1 2 ! 2 1 ? 1 2 ? 3 1 ! 1 2 |
Notes
In the sample test white balls are marked as 0, black ones — as 1. Let’s examine the sample closely.
First game: 01 → 01 → 10 → 01 — we did not guess correctly.
Second game: 101 → 011 → 110 — we guessed correctly.
In this test we have guessed correctly in one game out of two.
Problem Author: Alexey Danilyuk
Problem Source: Ural Regional School Programming Contest 2015
Tags: unusual problem (hide tags for unsolved problems)
Difficulty: 421
题意：有n个球，要么0，要么1，你先进行若干次操作，选择u，v，如果a[u]<a[v]，那么他们交换
以上操作无任何反馈
最后进行一个论断：你选择两个你认为相等的位置输出
正确80%以上即可。
分析：首先我们可以都过交换操作来个冒泡之类的排序
然后随机选择两个相邻的点，正确率为(n-2)/(n-1)
总的正确率80%应该没问题。
1 #include <iostream>
2 #include <ctime>
3 #include <cstdlib>
4 using namespace std;
5
6 int n;
7
8 int main()
9 {
10 ios::sync_with_stdio(0);
11 srand(time(0));
12 int m;
13 cin >> m;
14 for(int n = 2; n <= m + 1; n++)
15 {
16 for(int i = 2; i <= n; i++)
17 for(int j = 1; j < i; j++)
18 cout << "? " << j << ‘ ‘ << i << "\n";
19 int x = rand() % (n - 1) + 1;
20 cout << "! " << x << ‘ ‘ << x + 1 << "\n";
21 cout.flush();
22 }
23 return 0;
24 }