P6146 [USACO20FEB]Help Yourself G

https://www.luogu.com.cn/record/79815317

Luogu/P6146/P6146.cpp

@@ -0,0 +1,51 @@
+#include <iostream>
+#include <algorithm>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+const int mod = 1e9 + 7;
+
+int n, s[N << 1], f[N];
+std::pair<int, int> a[N];
+
+int pow(int a, int b) {
+    int res = 1;
+
+    while (b) {
+        if (b & 1) res = 1ll * res * a % mod;
+        a = 1ll * a * a % mod;
+        b >>= 1;
+    }
+
+    return res;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i].first >> a[i].second;
+
+        s[a[i].second]++;
+    }
+
+    std::sort(a + 1, a + 1 + n);
+
+    for (int i = 1; i <= n << 1; i++) {
+        s[i] += s[i - 1];
+    }
+
+    for (int i = 1; i <= n; i++) {
+        f[i] = (f[i - 1] * 2 % mod + pow(2, s[a[i].first - 1]) % mod) % mod;
+    }
+
+    cout << f[n] << endl;
+
+    return 0;
+}