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Người dùng hungnt_7I02425
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Giới thiệu
include <iostream>
using namespace std;
int n, x; long long dem[1000005];
int main() { ios_base::sync_with_stdio(false); cin.tie(NULL);
cin >> n >> x;
for (int i = 0; i < n; i++) {
int val;
cin >> val;
dem[val]++;
}
long long ans = 0;
for (int v = 0; v <= x / 2; v++) {
int remaining = x - v;
if (remaining > 1000000) continue;
if (v == remaining) {
ans += dem[v] * (dem[v] - 1) / 2 + dem[v];
} else {
ans += dem[v] * dem[remaining];
}
}
cout << ans << "\n";
return 0;
}