Day 7 q1

Author: Humanshere

Problems/Binary-Search/Day-07/sol/Solution1.cpp

@@ -0,0 +1,92 @@
+//problem link- https://codeforces.com/problemset/problem/1538/C
+//submission link- https://codeforces.com/problemset/submission/1538/356104640
+//approach- for every index find a lower index where possible pair value starts and ends unsing binary searches
+//time complexity- O(nlogn)
+#include <bits/stdc++.h>
+using namespace std;
+#define endl '\n'
+#define sp << " " <<
+#define int long long
+#define fora(a) for(auto i:a)
+#define gcd(a,b) __gcd(a,b)
+#define lcm(a,b) (a*(b/gcd(a,b)))
+#define forn(i,n) for(int i=0; i<n; i++)
+#define printv(a) {for(auto u:a) cout<<u<<" "; cout<<endl;}
+#define inputv(a) {for(int i=0;i<n;i++) cin>>a[i];}
+#define ll long long
+#define vi vector<int>
+#define vll vector<long long>
+#define pii pair<int, int>
+#define pll pair<long long, long long>
+#define all(x) x.begin(),x.end()
+
+void fast_io() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+    cout.tie(NULL);
+}
+
+
+const int MOD = 1e9 + 7;
+ll addMod(ll a, ll b) { return (a + b) % MOD; }
+ll subMod(ll a, ll b) { return (a - b + MOD) % MOD; }
+ll mulMod(ll a, ll b) { return (a * b) % MOD; }
+
+ll powerMod(ll a, ll b) {
+    ll res = 1;
+    while (b > 0) {
+        if (b & 1) res = mulMod(res, a);
+        a = mulMod(a, a);
+        b >>= 1;
+    }
+    return res;
+}
+
+
+
+
+
+void solve() {
+    int n,l,r;
+    cin>>n>>l>>r;
+    vi a(n);
+    inputv(a);
+    int ans=0;
+    sort(all(a));
+    for(int i=0;i<n;i++){
+        
+        auto it=lower_bound(a.begin(),a.begin()+i,l-a[i]);
+        int low=-1;
+        if (it!=a.begin()+i) {
+            low=it-a.begin();
+        } 
+
+        it =upper_bound(a.begin(),a.begin()+i,r-a[i]);
+        int high=-1;
+        if(it!=a.begin()) {
+            high=it-a.begin()-1;
+        } 
+        if(high!=-1&&low!=-1&&high>=low){
+            ans+=high-low+1;
+        }
+    }
+
+     cout<<ans<<endl;
+}
+
+
+
+
+
+signed main() {
+    fast_io();
+    
+    int t;
+    cin >> t;
+    
+    while (t--) {
+        solve();
+    }
+    
+    return 0;
+}