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The problem from Educational Codeforces Round 161 (Rated for Div. 2)

Browse Source 
https://codeforces.com/problemset/problem/1922/B

Signed-off-by: Frederick Chen <seventeen@ohdragonboi.cn>
This commit is contained in:
Frederick Chen 2025-04-19 10:27:27 +08:00
parent d1347b22c0
commit 10fe6aa33b
1 changed files with 19 additions and 0 deletions
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19
codeforces/solo-problems/1922B_Forming_Triangles.cpp Normal file
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#include<iostream>
using namespace std;
long long t, n, a[300005];
long long cnt[300005], s[300005], ans;
int main(){
ios::sync_with_stdio(0);
cin >> t;
while(t -- ){
cin >> n;
ans = 0;
for(int i = 0; i <= n; i ++ ) cnt[i] = s[i] = 0;
for(int i = 1; i <= n; i ++ ) cin >> a[i], cnt[a[i]] ++ ;
for(int i = 0; i <= n; i ++ ) ans += cnt[i] * (cnt[i] - 1) * (cnt[i] - 2) / 6, s[i] = (i == 0 ? 0 : s[i - 1]) + cnt[i];
for(int i = 1; i <= n; i ++ ) ans += cnt[i] * (cnt[i] - 1) / 2 * s[i-1];
cout << ans << "\n";
}
return 0;
}