From 8ba6ad7ebc29e77d3fcbcbca6c0628e2eda3349b Mon Sep 17 00:00:00 2001
From: Ren Baoshuo <i@baoshuo.ren>
Date: Sun, 8 Aug 2021 16:35:00 +0800
Subject: [PATCH] =?UTF-8?q?=E7=AC=AC=E4=B8=89=E5=B1=8A=E2=80=9C=E5=9B=BE?=
 =?UTF-8?q?=E7=81=B5=E6=9D=AF=E2=80=9D=E8=B6=A3=E5=91=B3=E7=BD=91=E7=BB=9C?=
 =?UTF-8?q?=E9=82=80=E8=AF=B7=E8=B5=9B=20(=E4=B8=AD=E7=BA=A7)?=
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---
 XJOI/contest/21med/A/A.cpp | 26 +++++++++++++++++++
 XJOI/contest/21med/B/B.cpp | 52 ++++++++++++++++++++++++++++++++++++++
 XJOI/contest/21med/C/C.cpp | 33 ++++++++++++++++++++++++
 3 files changed, 111 insertions(+)
 create mode 100644 XJOI/contest/21med/A/A.cpp
 create mode 100644 XJOI/contest/21med/B/B.cpp
 create mode 100644 XJOI/contest/21med/C/C.cpp

diff --git a/XJOI/contest/21med/A/A.cpp b/XJOI/contest/21med/A/A.cpp
new file mode 100644
index 00000000..66492909
--- /dev/null
+++ b/XJOI/contest/21med/A/A.cpp
@@ -0,0 +1,26 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int n, p;
+string s;
+stack<pair<char, int>> st;
+
+int main() {
+    cin >> n >> p >> s;
+    s = ' ' + s;
+    for (int i = 1; i < s.size(); i++) {
+        if (s[i] == '{') {
+            st.push(make_pair(s[i], i));
+        } else if (st.top().second == p) {
+            cout << i << endl;
+            exit(0);
+        } else if (i == p) {
+            cout << st.top().second << endl;
+            exit(0);
+        } else {
+            st.pop();
+        }
+    }
+    return 0;
+}
diff --git a/XJOI/contest/21med/B/B.cpp b/XJOI/contest/21med/B/B.cpp
new file mode 100644
index 00000000..6155eeae
--- /dev/null
+++ b/XJOI/contest/21med/B/B.cpp
@@ -0,0 +1,52 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int t, a, cnt, prime[100005];
+bool flag, is_prime[1000005];
+
+int eratosthenes(int n) {
+    int p = 0;
+    for (int i = 0; i <= n; i++) is_prime[i] = 1;
+    is_prime[0] = is_prime[1] = 0;
+    for (int i = 2; i <= n; i++) {
+        if (is_prime[i]) {
+            prime[p++] = i;
+            if (1ll * i * i <= n) {
+                for (int j = i * i; j <= n; j += i) {
+                    is_prime[j] = 0;
+                }
+            }
+        }
+    }
+    return p;
+}
+
+long long binpow(long long a, long long b, long long m) {
+    a %= m;
+    long long res = 1;
+    while (b > 0) {
+        if (b & 1) res = res * a % m;
+        a = a * a % m;
+        b >>= 1;
+    }
+    return res;
+}
+
+int main() {
+    cin >> t;
+    cnt = eratosthenes(1000000);
+    while (t--) {
+        flag = false;
+        cin >> a;
+        for (int i = 0; i < cnt; i++) {
+            if (binpow(a, prime[i], 10) % 10 == binpow(prime[i], a, 10) % 10) {
+                cout << prime[i] << endl;
+                flag = true;
+                break;
+            }
+        }
+        if (!flag) cout << -1 << endl;
+    }
+    return 0;
+}
diff --git a/XJOI/contest/21med/C/C.cpp b/XJOI/contest/21med/C/C.cpp
new file mode 100644
index 00000000..2a8b2846
--- /dev/null
+++ b/XJOI/contest/21med/C/C.cpp
@@ -0,0 +1,33 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int n;
+long long ans, cnt, x;
+pair<long long, long long> q[300005];
+
+bool cmp(pair<long long, long long> a, pair<long long, long long> b) {
+    return (a.first - b.first) * (a.second + b.second) > (a.first + b.first) * (a.second - b.second);
+}
+
+int main() {
+    cin >> n;
+    for (int i = 0; i < n; i++) {
+        cin >> q[i].first >> q[i].second;
+    }
+    sort(q, q + n, cmp);
+    for (int i = 0; i < n; i++) {
+        cnt += abs(2 * q[i].second * x + q[i].second * q[i].first);
+        x += q[i].first;
+    }
+    ans = max(ans, cnt);
+    x = 0;
+    cnt = 0;
+    for (int i = n - 1; i >= 0; i--) {
+        cnt += abs(2 * q[i].second * x + q[i].second * q[i].first);
+        x += q[i].first;
+    }
+    ans = max(ans, cnt);
+    cout << ans << endl;
+    return 0;
+}