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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.     	bool flag = false;
  66.         int l = 0 , r = n-1;
  67.         while(l<=r){
  68.             int mid = l+((r-l))/2;
  69.             if(mid==0){
  70.                 if(nums[mid]==nums[mid+1]){
  71.                     l = mid+1;
  72.                 }
  73.                 else{
  74.                 	flag = true;
  75.                     cout<<nums[mid]<<endl;
  76.                     break;
  77.                 }
  78.             }
  79.             if(mid<n-1 && mid>0){
  80.                 if(nums[mid]==nums[mid+1]){
  81.                     if(mid%2==0){
  82.                         l = mid+1;
  83.                     }
  84.                     else{
  85.                         r = mid-1;
  86.                     }
  87.                 }
  88.                 else if(nums[mid]==nums[mid-1]){
  89.                     if(mid%2==0){
  90.                         r = mid-1;
  91.                     }
  92.                     else{
  93.                         l = mid+1;
  94.                     }
  95.                 }
  96.                 else{
  97.                    flag = true;
  98.                    cout<<nums[mid]<<endl;
  99.                    break;
  100.                 }
  101.             }
  102.             else{
  103.                 if(nums[mid]==nums[mid-1]){
  104.                     r = mid-1;
  105.                 }
  106.                 else{
  107.                 	flag = true;
  108.                     cout<<nums[mid]<<endl;
  109.                     break;
  110.                 }
  111.             }
  112.         }
  113.         if(!flag){
  114.         cout<<-1<<endl;
  115.         }
  116.     }
  117. }
  118.  
  119. signed main(){
  120.     ios::sync_with_stdio(false); cin.tie(NULL);
  121.     int t;
  122.     cin >> t;
  123.     while(t--){
  124.         solve();
  125.     }
  126.     return 0;
  127. }
  128.  
  129.  
Success #stdin #stdout 0.01s 5308KB
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https://ideone.com/yKMF7Q
language:
C++14 (gcc 8.3)
created:
1 day ago
visibility:
public

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