38 lines
582 B
C++
38 lines
582 B
C++
#include <bits/stdc++.h>
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using namespace std;
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int a[500000];
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int main() {
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ios_base::sync_with_stdio(false);
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cin.tie(NULL);
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freopen("tgc.inp", "r", stdin);
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int n;
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cin >> n;
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for (int i = 0; i < n; i++)
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cin >> a[i];
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sort(a, a + n);
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int res = 0;
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for (int i = 0; i < n - 1; i++) {
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if (a[i] != a[i + 1])
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continue;
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int l = i, r = n - 1;
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int mid;
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while (l < r) {
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mid = (l + r) / 2;
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if (a[mid] < 2 * a[i]) {
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l = mid + 1;
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} else {
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r = mid;
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}
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}
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res += r - mid + l;
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}
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cout << res << "\n";
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}
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