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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. int consistency(int n, int k){
  34.  
  35. 	int ans = 0;
  36. 	int s = 0, e = n-1;
  37.  
  38. 	while(s<e){
  39. 		if(a[s] + a[e] > k){
  40. 			e--;
  41. 		}
  42. 		else if(a[s] + a[e] < k){
  43. 			s++;
  44. 		}
  45. 		else{
  46. 			int x = a[s];
  47. 			int ct1 = 0;
  48. 			while(s<=e && a[s] == x){
  49. 				ct1++;
  50. 				s++;
  51. 			}
  52.  
  53. 			int y = a[e];
  54. 			int ct2 = 0;
  55. 			while(e>=s && a[e] == y){
  56. 				ct2++;
  57. 				e--;
  58. 			}
  59.  
  60. 			if(x == y) ans += ct1*(ct1-1)/2;
  61. 			else ans += ct1*ct2;
  62. 		}
  63. 	}
  64. 	return ans;
  65. }
  66.  
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  81.  
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  84.  
  85.  
  86.  
  87.  
  88. int practice(int n){
  89.  
  90.  
  91.     return 0;
  92. }
  93.  
  94.  
  95.  
  96.  
  97.  
  98. void solve() {
  99.  
  100.     int n, k;
  101.     cin>> n >> k;
  102.  
  103.     a.resize(n);
  104.     for(int i=0; i<n; i++) cin >> a[i];
  105.  
  106.     cout << consistency(n, k) << endl;
  107.  
  108.  
  109. }
  110.  
  111.  
  112.  
  113.  
  114.  
  115. int32_t main() {
  116.     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  117.  
  118.     int t = 1;
  119.     // cin >> t;
  120.     while (t--) {
  121.         solve();
  122.     }
  123.  
  124.     return 0;
  125. }
Success #stdin #stdout 0s 5320KB
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https://ideone.com/EF7xYA
language:
C++14 (gcc 8.3)
created:
14 hours ago
visibility:
public

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