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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define int              long long int
  4. #define double           long double
  5. #define print(a)         for(auto x : a) cout << x << " "; cout << endl
  6.  
  7.  
  8. const int M = 1000000007;
  9. const int N = 3e5+9;
  10. const int INF = 2e9+1;
  11. const int LINF = 2000000000000000001;
  12.  
  13. inline int power(int a, int b, int mod=M) {
  14.     int x = 1;
  15.     a %= mod;
  16.     while (b) {
  17.         if (b & 1) x = (x * a) % mod; 
  18.         a = (a * a) % mod;
  19.         b >>= 1;
  20.     }
  21.     return x;
  22. }
  23.  
  24.  
  25. //_ ***************************** START Below *******************************
  26.  
  27. //* Change this to false => before submitting to cf
  28. // bool testing = true; 
  29. bool testing = false;
  30.  
  31.  
  32. vector<int> a;
  33.  
  34. void hack(int n){
  35.     a.resize(n+1);
  36.     for(int i=1; i<=n; i++) cin >> a[i];
  37. }
  38.  
  39. int  interactor(int i){
  40.     return a[i];
  41. }
  42.  
  43.  
  44.  
  45. int askQuery(int x){
  46.     cout << "? " << x << endl;
  47.  
  48.     if(testing){
  49.         cout << interactor(x) << endl;
  50.         return interactor(x);
  51.     }
  52.     int y;
  53.     cin >> y;
  54.     return y;
  55.  
  56. }
  57.  
  58.  
  59. int consistency(int n){
  60.  
  61.     if(testing){
  62.         hack(n);
  63.     }
  64.  
  65.     int s = 1, e = n;
  66.     int ans = -1;
  67.  
  68.     while(s<=e){
  69.         int mid = s + (e-s)/2;
  70.  
  71.  
  72.         int res = askQuery(mid);
  73.         int left = mid-1 == 0 ? INF : askQuery(mid-1);
  74.         int right = mid+1 == n+1 ? INF : askQuery(mid+1);
  75.  
  76.         if(left > res && res < right){
  77.             ans = mid;
  78.             break;
  79.         }
  80.         if(left > res ){
  81.             s = mid+1;
  82.         }
  83.         else{
  84.             e = mid-1;
  85.         }
  86.  
  87.     }
  88.  
  89.     return ans;
  90. }
  91.  
  92.  
  93.  
  94.  
  95.  
  96.  
  97.  
  98.  
  99. void solve() {
  100.     int n;
  101.     cin >> n;
  102.  
  103.     int ans = consistency(n);
  104.     cout << "! " << ans << endl;
  105.  
  106. }
  107.  
  108.  
  109.  
  110.  
  111.  
  112. int32_t main() {
  113.     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  114.  
  115.     int t = 1;
  116.     // cin >> t;
  117.     while(t--){
  118.         solve();
  119.     }
  120.  
  121.  
  122.     return 0;
  123. }
Success #stdin #stdout 0s 5320KB
comments (?)
stdin
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11
2 4 3 7 10 11 1 9 8 6 5
stdout
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? 6
11
? 5
10
? 7
1
? 3
3
? 2
4
? 4
7
! 3
https://ideone.com/X0RTRp
language:
C++14 (gcc 8.3)
created:
9 hours ago
visibility:
public

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