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Codeforces Round 1042 (Div. 3)/F. Unjust Binary Life.cpp

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+/* Problem URL: https://codeforces.com/contest/2131/problem/F */
+
+#include <bits/stdc++.h>
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/pb_ds/tree_policy.hpp>
+
+using namespace std;
+using namespace __gnu_pbds;
+
+template <class T, class comp = less<>>
+using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;
+
+#define V vector
+
+#define rmin(a, b) a = min(a, b)
+#define rmax(a, b) a = max(a, b)
+
+#define rep(i, lim) for (int i = 0; i < (lim); i++)
+#define nrep(i, s, lim) for (int i = s; i < (lim); i++)
+
+#define repv(i, v) for (auto &i : (v))
+#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
+#define sortv(v) sort(v.begin(), v.end())
+#define all(v) (v).begin(), (v).end()
+
+using vi = vector<int>;
+using vvi = vector<vi>;
+using vvvi = vector<vvi>;
+using vvvvi = vector<vvvi>;
+
+using ll = long long;
+
+using vl = vector<ll>;
+using vvl = vector<vl>;
+using vvvl = vector<vvl>;
+using vvvvl = vector<vvvl>;
+
+template<class v>
+auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
+    os << vec[0];
+    for (size_t i = 1; i < vec.size(); i++) {
+        os << ' ' << vec[i];
+    }
+    os << '\n';
+    return os;
+}
+
+template<class v>
+auto operator>>(istream &is, vector<v> &vec)->istream& {
+    for (auto &i : vec) {
+        is >> i;
+    }
+    return is;
+}
+
+template<class v>
+auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
+    for (auto &i : vec) {
+        os << i[0];
+        for (size_t j = 1; j < i.size(); j++) {
+            os << ' ' << i[j];
+        }
+        os << '\n';
+    }
+    return os;
+}
+
+template<class v>
+auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
+    for (auto &i : vec) {
+        for (auto &j : i) {
+            is >> j;
+        }
+    }
+    return is;
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int t;
+    cin >> t;
+    while (t--) {
+        ll n;
+        cin >> n;
+
+        string at, bt;
+        cin >> at >> bt;
+
+        vi a(n);
+        vi b(n);
+
+        rep(i, n) {
+            a[i] = at[i] - '0';
+            b[i] = bt[i] - '0';
+        }
+
+        vl minimal(n * 2 + 2);
+        vl count(n * 2 + 2);
+
+        int middle = n;
+        vi bc(2);
+
+        rep(i, n) {
+            bc[b[i]]++;
+
+            int diff = bc[0] - bc[1];
+
+            minimal[middle + diff] += min(bc[0], bc[1]);
+            count[middle + diff]++;
+        }
+
+        nrep(i, 2, n + 1) {
+            minimal[middle + i] += minimal[middle + i - 1];
+            minimal[middle - i] += minimal[middle - i + 1];
+            count[middle + i] += count[middle + i - 1];
+            count[middle - i] += count[middle - i + 1];
+        }
+
+        vl ac(2);
+        ll ans = 0;
+
+        rep(i, n) {
+            ac[a[i]]++;
+
+            int diff = ac[1] - ac[0];
+
+            ans += minimal[middle + diff] + count[middle + diff] * min(ac[1], ac[0]);
+        }
+
+        cout << ans << '\n';
+    }
+}