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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. #define endl '\n'
  4. #define int long long
  5. const int MOD = pow(10,9)+7;
  6. const int MOD2 = 998244353;
  7. const int INF = LLONG_MAX/2;
  8.  
  9. int primes[1000000];
  10.  
  11. void seive(){
  12.     fill(primes, primes + 1000000, 1);
  13.     primes[0] = primes[1] = 0;
  14.     for(int i = 2 ; i*i < 1000000 ; i++){
  15.         if(primes[i]){
  16.             for(int j = i*i ; j < 1000000 ; j += i){
  17.                 primes[j] = 0;
  18.             }
  19.         }
  20.     }
  21.     for(int i = 1 ; i < 1000000 ; i++){
  22.         primes[i] += primes[i-1];
  23.     }
  24. }
  25. int factorial(int n){
  26.     if(n==0){
  27.         return 1;
  28.     }
  29.     return (n*(factorial(n-1)))%MOD;
  30. }
  31. bool isPrime(int n){
  32.     if(n <= 1) return false;
  33.     for(int i = 2 ; i*i <= n ; i++){
  34.         if(n % i == 0) return false;
  35.     }
  36.     return true;
  37. }
  38.  
  39. int power(int a, int b){
  40.     if(b == 0) return 1;
  41.     a %= MOD;
  42.     int value = power(a, b / 2);
  43.     if(b % 2 == 0){
  44.         return (value * value) % MOD;
  45.     } else {
  46.         return ((value * value) % MOD * (a % MOD)) % MOD;
  47.     }
  48. }
  49.  
  50. int gcd(int a, int b){
  51.     if(a == 0) return b;
  52.     return gcd(b % a, a);
  53. }
  54. void solve() {
  55.     int n;
  56.     cin>>n;
  57.     int nums[n];
  58.     for(int i = 0 ; i<n ; i++){
  59.         cin>>nums[i];
  60.     }
  61.     if(n==1){
  62.         cout<<nums[0]<<endl;
  63.     }
  64.     else{
  65.         int l = 0 , r = n-1;
  66.         while(l<=r){
  67.             int mid = l+((r-l))/2;
  68.             if(mid==0){
  69.                 if(nums[mid]==nums[mid+1]){
  70.                     l = mid+1;
  71.                 }
  72.                 else{
  73.                     cout<<nums[mid]<<endl;
  74.                     break;
  75.                 }
  76.             }
  77.             if(mid<n-1 && mid>0){
  78.                 if(nums[mid]==nums[mid+1]){
  79.                     if(mid%2==0){
  80.                         l = mid+1;
  81.                     }
  82.                     else{
  83.                         r = mid-1;
  84.                     }
  85.                 }
  86.                 else if(nums[mid]==nums[mid-1]){
  87.                     if(mid%2==0){
  88.                         r = mid-1;
  89.                     }
  90.                     else{
  91.                         l = mid+1;
  92.                     }
  93.                 }
  94.                 else{
  95.                    cout<<nums[mid]<<endl;
  96.                    break;
  97.                 }
  98.             }
  99.             else{
  100.                 if(nums[mid]==nums[mid-1]){
  101.                     r = mid-1;
  102.                 }
  103.                 else{
  104.                     cout<<nums[mid]<<endl;
  105.                     break;
  106.                 }
  107.             }
  108.         }
  109.         cout<<-1<<endl;
  110.     }
  111. }
  112.  
  113. signed main(){
  114.     ios::sync_with_stdio(false); cin.tie(NULL);
  115.     //int t;
  116.     //cin >> t;
  117.     //while(t--){
  118.         solve();
  119.     //}
  120.     return 0;
  121. }
  122.  
  123.  
Success #stdin #stdout 0.01s 5324KB
comments (?)
stdin 
2
9
1 1 2 3 3 4 4 8 8
7
3 3 7 7 10 11 11
stdout 
9
-1
https://ideone.com/bkO4Gr
language:
C++14 (gcc 8.3)
created:
1 day ago
visibility:
public

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