CF1190D Tokitsukaze and Strange Rectangle

思路：

线段树 + 扫描线。

实现：

 #include <bits/stdc++.h>
 using namespace std;
 typedef long long ll;
 const int N = ;
 int n, x[N], y[N], bit[N];
 vector<int> v[N];
 void compress(vector<int>& x)
 {
     sort(x.begin(), x.end());
     x.erase(unique(x.begin(), x.end()), x.end());
 }
 int lowbit(int x) { return x & -x; }
 void add(int i, int x)
 {
     while (i <= n) { bit[i] += x; i += lowbit(i); }
 }
 int sum(int i)
 {
     int ans = ;
     while (i) { ans += bit[i]; i -= lowbit(i); }
     return ans;
 }
 int main()
 {
     while (cin >> n)
     {
         memset(bit, , sizeof bit);
         for (int i = ; i <= n; i++) v[i].clear();
         vector<int> vx, vy;
         for (int i = ; i <= n; i++)
         {
             cin >> x[i] >> y[i];
             vx.push_back(x[i]); vy.push_back(y[i]);
         }
         compress(vx); compress(vy);
         for (int i = ; i <= n; i++)
         {
             x[i] = lower_bound(vx.begin(), vx.end(), x[i]) - vx.begin() + ;
             y[i] = lower_bound(vy.begin(), vy.end(), y[i]) - vy.begin() + ;
             v[y[i]].push_back(x[i]);
         }
         ll ans = ;
         for (int i = n; i >= ; i--)
         {
             sort(v[i].begin(), v[i].end());
             for (int j = ; j < v[i].size(); j++)
             {
                 int t = v[i][j];
                 if (sum(t) - sum(t - )) continue;
                 add(t, );
             }
             int prev = ;
             for (int j = ; j < v[i].size(); j++)
             {
                 int t = v[i][j];
                 ans += 1ll * (sum(t - ) - sum(prev) + ) * (sum(n) - sum(t) + );
                 prev = t;
             }
         }
         cout << ans << endl;
     }
     return ;
 }