feat(cses); refactor structure

codeforces/835/e.cc

@@ -0,0 +1,68 @@
+#include <bits/stdc++.h>  // {{{
+
+// https://codeforces.com/blog/entry/96344
+
+#pragma GCC optimize("O2,unroll-loops")
+#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
+
+using namespace std;
+
+using i32 = int32_t;
+using u32 = uint32_t;
+using i64 = int64_t;
+using u64 = uint64_t;
+using f64 = double;
+using f128 = long double;
+//  }}}
+
+void solve() {
+  u32 n;
+  cin >> n;
+  vector<u32> a(n);
+  for (u32 i = 0; i < n; ++i) {
+    cin >> a[i];
+  }
+
+  vector<i64> prefix_one(n + 1, 0), postfix_zero(n + 2, 0);
+  for (u32 i = 0; i < n; ++i) {
+    prefix_one[i + 1] = (a[i] == 1) + prefix_one[i];
+  }
+  for (i32 i = n - 1; i >= 0; --i) {
+    postfix_zero[i + 1] = postfix_zero[i + 2] + (a[i] == 0);
+  }
+  postfix_zero[0] = postfix_zero[1];
+
+  i64 ans = 0;
+  for (u32 i = 0; i < n; ++i) {
+    if (a[i] == 1)
+      ans += postfix_zero[i + 2];
+  }
+  i64 init = ans;
+
+  for (u32 i = 0; i < n; ++i) {
+    if (a[i] == 0)
+      ans = max(ans, init + postfix_zero[i + 2] - prefix_one[i]);
+    else if (a[i] == 1)
+      ans = max(ans, init + prefix_one[i] - postfix_zero[i + 2]);
+    // } else {  // NOTE: forgot 0->1 is possible
+    // }
+  }
+
+  cout << ans << '\n';
+}
+
+int main() {  // {{{
+  cin.tie(nullptr)->sync_with_stdio(false);
+  cin.exceptions(cin.failbit);
+
+  int tc = 1;
+  cin >> tc;
+
+  for (int t = 0; t < tc; ++t) {
+    solve();
+  }
+
+  return 0;
+}
+// }}}
+