[C++知识库]C. Guess the Array

// Problem: C. Guess the Array
// Contest: Codeforces - Technocup 2017 - Elimination Round 1 (Unofficially Open for Everyone, Rated for Div. 2)
// URL: https://codeforces.com/problemset/problem/727/C
// Memory Limit: 256 MB
// Time Limit: 1000 ms
// 2022-03-15 22:55:20
// 
// Powered by CP Editor (https://cpeditor.org)

#include<bits/stdc++.h>
using namespace std;

#define rep(i,l,r) for(int i=(l);i<=(r);i++)
#define per(i,l,r) for(int i=(l);i>=(r);i--)
#define ll long long
#define mset(s,t) memset(s,t,sizeof(t))
#define mcpy(s,t) memcpy(s,t,sizeof(t))
#define fi first
#define se second
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define SZ(x) ((int)(x).size())
#define mp make_pair

typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;   
typedef vector<ll> Vll;               
typedef vector<pair<int, int> > vpii;
typedef vector<pair<ll, ll> > vpll;                        

const ll mod = 1e9 + 7;
//const ll mod = 998244353;
const double pi  = acos(-1.0);

inline ll qmi (ll a, ll b) {
	ll ans = 1;
	while (b) {
		if (b & 1) ans = ans * a%mod;
		a = a * a %mod;
		b >>= 1;
	}
	return ans;
}
inline int read () {
	int x = 0, f = 0;
	char ch = getchar();
	while (!isdigit(ch)) f |= (ch=='-'),ch= getchar();
	while (isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
	return f?-x:x;
}
template<typename T> void print(T x) {
	if (x < 0) putchar('-'), x = -x;
	if (x >= 10) print(x/10);
	putchar(x % 10 + '0');
}
inline ll sub (ll a, ll b) {
	return ((a - b ) %mod + mod) %mod;
}
inline ll add (ll a, ll b) {
	return (a + b) %mod;
}
inline ll inv (ll a) {
	return qmi(a, mod - 2);
}
int get (int i, int j) {
	cout <<"?" << ' ' << i << ' ' << j << endl;
	int x;
	cin >> x;
	return x;
}
void solve() {
	int n;
	cin >> n;
	int sum[100005] = {0};
	int st[100005] = {0};
	int idx = 0;
	for (int i = 2; i <= 3; i ++) {
		sum[++idx] = get (1, i);
	}
	sum[++idx] = get (2, 3);
	int dif1 = (sum[1] - sum[2] + sum[3]) / 2;
	st[2] = dif1;
	st[1] = sum[1] - dif1;
	st[3] = sum[3] - st[2];
	for (int i = 4; i <= n; i ++) {
		int x = get (i - 1, i);
		st[i] = x - st[i - 1];
	}
	cout << "! ";
	for (int i = 1; i <= n; i ++)
		cout << st[i] << ' ';
	puts("");
	
}
int main () {
	// ios::sync_with_stdio(0),cin.tie(0), cout.tie(0);
    int t;
    t =1;
    //cin >> t;
    while (t --) solve();
    return 0;
}

子问题 a[1] + a[2] = b[1] a[1] + a[3] = b[2]; a[2] + a[3] = b[3]; 可以求出a[1], a[2], a[3]; 然后再每一次循环i - 1, i