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CP01031.cpp
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CP01031.cpp
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#include <bits/stdc++.h>
using namespace std;
using namespace std;
int check(vector<int> a, int n, int sum)
{
int l, r;
sort(a.begin(), a.end());
int ans = 0;
// Every iteration of loop counts triplet with
// first element as arr[i].
for (int i = 0; i < n - 2; i++)
{
// Initialize other two elements as corner elements
// of subarray arr[j+1..k]
int j = i + 1, k = n - 1;
// Use Meet in the Middle concept
while (j < k)
{
// If sum of current triplet is more or equal,
// move right corner to look for smaller values
if (a[i] + a[j] + a[k] >= sum)
k--;
// Else move left corner
else
{
// This is important. For current i and j, there
// can be total k-j third elements.
ans += (k - j);
j++;
}
}
}
return ans;
}
int main()
{
int t;
cin >> t;
while (t--)
{
int n, K;
cin >> n >> K;
vector<int> a;
for (int i = 0; i < n; ++i)
{
int tmp;
cin >> tmp;
a.push_back(tmp);
}
sort(a.begin(), a.end());
cout<<check(a, n, K);
cout << endl;
}
return 0;
}
/**
* @brief https://www.geeksforgeeks.org/count-triplets-with-sum-smaller-that-a-given-value/
*
*/