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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. inline int power(int a, int b) {
  6.     int x = 1;
  7.     while (b) {
  8.         if (b & 1) x *= a;
  9.         a *= a;
  10.         b >>= 1;
  11.     }
  12.     return x;
  13. }
  14.  
  15.  
  16. const int M = 1000000007;
  17. const int N = 3e5+9;
  18. const int INF = 2e9+1;
  19. const int LINF = 2000000000000000001;
  20.  
  21. //_ ***************************** START Below *******************************
  22.  
  23.  
  24.  
  25. vector<int> a;
  26.  
  27.  
  28. int consistency1(int n, int k) {
  29.  
  30. 	int  s= 0, e = n-1;
  31. 	int ans = 0;
  32.  
  33. 	//* keep in mind  s<e   (Not s<=e )
  34. 	while(s<e){
  35. 		int sum = a[s] + a[e];
  36. 		if(sum > k){
  37. 			ans += (e-s);
  38. 			e--;
  39. 		}
  40. 		else{
  41. 			s++;
  42. 		}
  43. 	}
  44.  
  45. 	return ans;
  46.  
  47. }
  48.  
  49.  
  50. //* Template 2
  51.  
  52. //* Think it as Reverse sliding window , 
  53. //* 	Expand Valid window => 
  54. //* 		sum > k 
  55. //* 		e is decreasing (instead of increasing ) 
  56.  
  57. //* 	Shrink Invalid window => sum <= k
  58.  
  59. int consistency2(int n, int k) {
  60.  
  61. 	int  s= 0, e = n-1;
  62. 	int ans = 0;
  63.  
  64.  
  65. 	while(e>=0){
  66. 		int sum = a[s] + a[e];
  67.  
  68. 		//* Invalid window : Shrink (cache invalidation style)
  69. 		while(s<e && a[s]+a[e] <= k) s++;
  70. 		if(s==e) break;
  71.  
  72. 		//* Valid window : Expand (e-- here)
  73. 		ans += (e-s);
  74. 		e--;
  75. 	}
  76.  
  77. 	return ans;
  78.  
  79. }
  80.  
  81.  
  82.  
  83.  
  84.  
  85.  
  86.  
  87.  
  88.  
  89.  
  90.  
  91.  
  92. int practice(int n, int k) {
  93. 	int ans = 0;
  94.  
  95. 	int s = 0, e = n-1;
  96. 	while(e>s){
  97. 		while(s<e && a[s]+a[e] <= k) s++;
  98. 		ans += e-s;
  99. 		e--;
  100. 	}
  101.  
  102. 	return ans;
  103.  
  104. }
  105.  
  106.  
  107.  
  108. void solve() {
  109.  
  110. 	int n, k;
  111. 	cin >> n >> k;
  112.  
  113. 	a.resize(n);
  114. 	for(int i=0; i<n; i++) cin >> a[i];
  115.  
  116.     // cout << consistency1(n, k) << " " <<  consistency2(n, k) << endl;
  117.  
  118.     cout << consistency1(n, k) << " -> " << practice(n, k) << endl;
  119. }
  120.  
  121.  
  122.  
  123.  
  124.  
  125. int32_t main() {
  126.     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  127.  
  128.     int t = 1;
  129.     // cin >> t;
  130.     while (t--) {
  131.         solve();
  132.     }
  133.  
  134.     return 0;
  135. }
Success #stdin #stdout 0s 5316KB
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5 8
1 2 7 9 10
stdout
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8 -> 8
https://ideone.com/3PAe5e
language:
C++14 (gcc 8.3)
created:
3 days ago
visibility:
public

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