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Codeforces Round 995 (Div. 3)/D. Counting Pairs.cpp

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+/* Problem URL: https://codeforces.com/contest/2051/problem/D */
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+#define V vector
+
+#define rmin(a, b) a = min(a, b)
+#define rmax(a, b) a = max(a, b)
+
+#define rep(i, lim) for (size_t i = 0; i < (lim); i++)
+#define nrep(i, s, lim) for (size_t i = s; i < (lim); i++)
+
+#define repv(i, v) for (auto &i : (v))
+#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
+#define sortv(v) sort(v.begin(), v.end())
+#define all(v) (v).begin(), (v).end()
+
+using vi = vector<int>;
+using vvi = vector<vi>;
+using vvvi = vector<vvi>;
+using vvvvi = vector<vvvi>;
+
+using ll = long long;
+
+using vl = vector<ll>;
+using vvl = vector<vl>;
+using vvvl = vector<vvl>;
+using vvvvl = vector<vvvl>;
+
+template<class v>
+auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
+    os << vec[0];
+    for (size_t i = 1; i < vec.size(); i++) {
+        os << ' ' << vec[i];
+    }
+    os << '\n';
+    return os;
+}
+
+template<class v>
+auto operator>>(istream &is, vector<v> &vec)->istream& {
+    for (auto &i : vec) {
+        is >> i;
+    }
+    return is;
+}
+
+template<class v>
+auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
+    for (auto &i : vec) {
+        os << i[0];
+        for (size_t j = 1; j < i.size(); j++) {
+            os << ' ' << i[j];
+        }
+        os << '\n';
+    }
+    return os;
+}
+
+template<class v>
+auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
+    for (auto &i : vec) {
+        for (auto &j : i) {
+            is >> j;
+        }
+    }
+    return is;
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int t;
+    cin >> t;
+    while (t--) {
+        ll n, x, y;
+        cin >> n >> x >> y;
+
+        vl items(n);
+        ll total = 0;
+        repv(i, items) {
+            cin >> i;
+            total += i;
+        }
+        sortv(items);
+        
+        ll count = 0;
+
+        ll ans = 0;
+        for (size_t i = n - 1; i > 0; i--) {
+            int low = 0;
+            int high = i - 1;
+            int ansx = -1;
+            ll tmp = total - items[i];
+            while (low <= high) {
+                int mid = (low + high) / 2;
+                
+                if (tmp - items[mid] >= x) {
+                    ansx = mid;
+                    low = mid + 1;
+                    continue;
+                }
+
+                high = mid - 1;
+            }
+
+            if (ansx == -1) {
+                continue;
+            }
+
+            low = 0;
+            high = i - 1;
+            int ansy = -1;
+            while (low <= high) {
+                int mid = (low + high) / 2;
+
+                if (tmp - items[mid] <= y) {
+                    ansy = mid;
+                    high = mid - 1;
+                    continue;
+                }
+
+                low = mid + 1;
+            }
+
+            if (ansy == -1) {
+                continue;
+            }
+
+            ans += (ansx - ansy) + 1;
+        }
+        cout << ans << '\n';
+    }
+}