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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.  
  28.  
  29.  
  30. vector<int> a;
  31.  
  32.  
  33.  
  34. //* Hashing Pairing
  35.  
  36. int kSumPairs1(vector<int>& a, int n, int k){
  37.  
  38. 	int ans = 0;
  39.  
  40. 	unordered_map<int,int> mp;
  41. 	for(int i=0; i<n; i++){
  42. 		if(mp.count(k-a[i])){
  43. 			ans++;
  44. 			mp[k-a[i]]--;
  45. 		    if(mp[k-a[i]] == 0)  	mp.erase(k-a[i]);
  46. 		}
  47. 		else mp[a[i]]++;
  48. 	}
  49.  
  50. 	return ans;
  51. }
  52.  
  53. int consistency1(int n){
  54. 	if(n<=1) return 0;
  55.  
  56. 	int ans = 0;
  57.  
  58. 	for(int i=0; i<n; i++){
  59. 		for(int j=i+1; j<n; j++){
  60. 			ans = max(ans, kSumPairs1(a, n, a[i]+a[j]));
  61. 		}
  62. 	}
  63.  
  64.  
  65. 	return ans;
  66. }
  67.  
  68.  
  69.  
  70.  
  71.  
  72. //* 2 PTr
  73.  
  74. int kSumPairs2(vector<int>& a, int n, int k){
  75.  
  76. 	int ans = 0;
  77. 	int s = 0, e = n-1;
  78.  
  79. 	while(s<e){
  80. 		if(a[s] + a[e] > k){
  81. 			e--;
  82. 		}
  83. 		else if(a[s] + a[e] < k){
  84. 			s++;
  85. 		}
  86. 		else{
  87. 			ans++;
  88. 			s++;
  89. 			e--;
  90. 		}
  91. 	}
  92. 	return ans;
  93. }
  94.  
  95.  
  96. int consistency2(int n){
  97. 	if(n<=1) return 0;
  98.  
  99. 	sort(begin(a), end(a));
  100.  
  101. 	int ans = 0;
  102.  
  103. 	for(int i=0; i<n; i++){
  104. 		for(int j=i+1; j<n; j++){
  105. 			ans = max(ans, kSumPairs2(a, n, a[i]+a[j]));
  106. 		}
  107. 	}
  108.  
  109.  
  110. 	return ans;
  111. }
  112.  
  113.  
  114.  
  115.  
  116.  
  117.  
  118.  
  119.  
  120.  
  121.  
  122. int practice(int n){
  123.  
  124.  
  125.     return 0;
  126. }
  127.  
  128.  
  129.  
  130.  
  131.  
  132. void solve() {
  133.  
  134.     int n;
  135.     cin>> n;
  136.  
  137.     a.resize(n);
  138.     for(int i=0; i<n; i++) cin >> a[i];
  139.  
  140.     cout << consistency1(n) <<  " " << consistency2(n) << endl;
  141.  
  142.  
  143. }
  144.  
  145.  
  146.  
  147.  
  148.  
  149. int32_t main() {
  150.     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  151.  
  152.     int t = 1;
  153.     // cin >> t;
  154.     while (t--) {
  155.         solve();
  156.     }
  157.  
  158.     return 0;
  159. }
Success #stdin #stdout 0s 5324KB
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https://ideone.com/muyx6v
language:
C++14 (gcc 8.3)
created:
1 day ago
visibility:
public

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