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Codeforces Round 447 (Div. 2)/A. QAQ.cpp

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+/* Problem URL: https://codeforces.com/problemset/problem/894/A */
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+#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);
+
+    string a;
+    cin >> a;
+
+    vi dp1(a.size());
+    vi dp2(a.size());
+    vi dp3(a.size());
+
+    dp1[0] = a[0] == 'Q';
+
+    nrep(i, 1, a.size()) {
+        if (a[i] == 'Q') {
+            dp1[i]++;
+            dp3[i] += dp2[i - 1];
+        
+        }
+
+        if (a[i] == 'A') {
+            dp2[i] += dp1[i - 1];
+        }
+
+        dp1[i] += dp1[i - 1];
+        dp2[i] += dp2[i - 1];
+        dp3[i] += dp3[i - 1];
+    }
+
+    cout << dp3.back() << '\n';
+}