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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. // 12
  28. // 1 2 5 3 4 7 9 8 3 4 1 6
  29.  
  30.  
  31.  
  32. vector<int> a;
  33.  
  34.  
  35.  
  36. //* Hashing Pairing
  37.  
  38. int kSumPairs(vector<int>& a, int n, int k){
  39.  
  40. 	int ans = 0;
  41.  
  42. 	unordered_map<int,int> mp;
  43. 	for(int i=0; i<n; i++){
  44. 		if(mp.count(k-a[i])){
  45. 			ans++;
  46. 			mp[k-a[i]]--;
  47. 		    if(mp[k-a[i]] == 0)  	mp.erase(k-a[i]);
  48. 		}
  49. 		else mp[a[i]]++;
  50. 	}
  51.  
  52. 	return ans;
  53. }
  54.  
  55. int consistency(int n){
  56. 	if(n<=1) return 0;
  57.  
  58. 	int ans = 0;
  59.  
  60. 	for(int i=0; i<n; i++){
  61. 		for(int j=i+1; j<n; j++){
  62. 			ans = max(ans, kSumPairs(a, n, a[i]+a[j]));
  63. 		}
  64. 	}
  65.  
  66.  
  67. 	return ans;
  68. }
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  90.  
  91.  
  92.  
  93. int practice(int n){
  94.  
  95.  
  96.     return 0;
  97. }
  98.  
  99.  
  100.  
  101.  
  102.  
  103. void solve() {
  104.  
  105.     int n;
  106.     cin>> n;
  107.  
  108.     a.resize(n);
  109.     for(int i=0; i<n; i++) cin >> a[i];
  110.  
  111.     cout << consistency(n)  << endl;
  112.  
  113.  
  114. }
  115.  
  116.  
  117.  
  118.  
  119.  
  120. int32_t main() {
  121.     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  122.  
  123.     int t = 1;
  124.     // cin >> t;
  125.     while (t--) {
  126.         solve();
  127.     }
  128.  
  129.     return 0;
  130. }
Success #stdin #stdout 0.01s 5280KB
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stdin
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12
1 2 5 3 4 7 9 8 3 4 1 6
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4
https://ideone.com/RRasVx
language:
C++14 (gcc 8.3)
created:
3 days ago
visibility:
public

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