Technocup 2017 ER1 C. Guess the Array

C. Guess the Array
time limit per test:1 second
memory limit per test:256 megabytes
input:standard input
output:standard output
This is an interactive problem. You should use flush operation after each printed line. For example, in C++ you should use fflush(stdout), in Java you should use System.out.flush(), and in Pascal — flush(output).

In this problem you should guess an array a which is unknown for you. The only information you have initially is the length n of the array a.

The only allowed action is to ask the sum of two elements by their indices. Formally, you can print two indices i and j (the indices should be distinct). Then your program should read the response: the single integer equals to ai + aj.

It is easy to prove that it is always possible to guess the array using at most n requests.

Write a program that will guess the array a by making at most n requests.

Interaction
In each test your program should guess a single array.

The input starts with a line containing integer n (3 ≤ n ≤ 5000) — the length of the array. Your program should read it at first.

After that your program should print to the standard output the requests about the sum of two elements or inform that the array is guessed.

In case your program is making a request to ask the sum of two elements, it should print line in the format “? i j” (i and j are distinct integers between 1 and n), where i and j are indices in the array a.
In case your program informs that the array is guessed, it should print line in the format “! a1 a2 … an” (it is guaranteed that all ai are positive integers not exceeding 105), where ai is the i-th element of the array a.
The response on a request is a single integer equal to ai + aj, printed on a separate line.

Your program can do at most n requests. Note that the final line «! a1 a2 … an» is not counted as a request.

Do not forget about flush operation after each printed line.

After you program prints the guessed array, it should terminate normally.

Example
input
5

9

7

9

11

6

output

? 1 5

? 2 3

? 4 1

? 5 2

? 3 4

! 4 6 1 5 5
Note
The format of a test to make a hack is:

The first line contains an integer number n (3 ≤ n ≤ 5000) — the length of the array.
The second line contains n numbers a1, a2, …, an (1 ≤ ai ≤ 105) — the elements of the array to guess.

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这题很水….
可以先问$(1,2)(2,3)(1,3)$得到1，2，3然后直接问$(1,i)$，得出每一个i
也可以依次问$(1,2)(2,3)(3,4).....(n-1,n)(n,1)$
得到n个方程快速求解

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int maxn = 5000 + 8;

queue<LL> que;

int main()
{
    int T = 1;
    while(T--){

    LL n, x12, x23, x13, res, xi_1i;
    cin >> n;


    cout << "? " << 1 << " " << 2 << "\n";
    fflush(stdout);
    cin >> x12;

    cout << "? " << 2 << " " << 3 << "\n";
    fflush(stdout);
    cin >> x23;

    cout << "? " << 1 << " " << 3 << "\n";
    fflush(stdout);
    cin >> x13;

    res = (x12 - x23 + x13) / 2;
    que.push(res);
    res = x12 - res;
    que.push(res);
    res = x23 - res;
    que.push(res);

    for(int i = 4; i <= n; i++){
        cout << "? " << i - 1 << " " << i << "\n";
        fflush(stdout);
        cin >> xi_1i;
        res = xi_1i - res;
        que.push(res);
    }
    cout << "!";
    fflush(stdout);
    while(!que.empty()){
        cout << " " << que.front();
        fflush(stdout);
        que.pop();
    }
    cout << endl;
    }
    return 0;
}