Merge pull request #442 from suzzzal/day07sol01

Day07sol01

Author: zonedoutdg

Problems/Binary-Search/Day-07/sol/suzzzal/day07sol01.cpp

@@ -0,0 +1,59 @@
+// submisiion link - https://codeforces.com/problemset/submission/1538/356092904
+
+/*
+ * APPROACH:
+ * First, sort all the numbers from smallest to largest so it's easier to find pairs.
+ * Then, for each number, search quickly (using binary search) for other bigger numbers 
+ * that can be added to it to make a sum between 'l' and 'r'. Count them up!
+ */
+
+ 
+#include <bits/stdc++.h>
+using namespace std;
+ 
+ 
+void solve() {
+    int n;
+    long long l, r;
+    cin >> n >> l >> r;
+ 
+ 
+    vector<long long> a(n);
+    for (int i = 0; i < n; i++) {
+        cin >> a[i];
+    }
+ 
+    sort(a.begin(), a.end());
+    long long count = 0;
+ 
+    for (int i = 0; i < n; i++) {
+ 
+        auto start_ptr = a.begin() + i + 1;
+        auto end_ptr = a.end();
+        auto low = lower_bound(start_ptr, end_ptr, l - a[i]);
+        auto high = upper_bound(start_ptr, end_ptr, r - a[i]);
+ 
+        count += (high - low);
+ 
+    }
+ 
+    cout << count << endl;
+ 
+}
+ 
+ 
+ 
+int main() {
+ 
+    int t;
+    cin >> t;
+    while (t--) {
+        solve();
+ 
+    }
+ 
+ 
+ 
+    return 0;
+ 
+}