upload some new code

FZOI/银行卡.cpp

@@ -0,0 +1,61 @@
+#include <bits/stdc++.h>
+#define int long long
+#define endl "\n"
+#define IMX LONG_LONG_MAX
+#define IMN LONG_LONG_MIN
+using namespace std;
+
+/* toothless. #17 */
+
+int n, pre, len;
+string s;
+
+int f(int n)
+{
+    int sum = 0;
+    while (n)
+    {
+        sum += n % 10;
+        n /= 10;
+    }
+    return sum;
+}
+
+int Get_ans(string s)
+{
+    int cnt = 0, sum = 0;
+    for (int i = len - 2; i >= 0; i--)
+    {
+        ++cnt;
+        if (cnt & 1)
+            sum += f((s[i] - '0') * 2);
+        else
+            sum += s[i] - '0';
+    }
+    return sum * 9 % 10;
+}
+
+signed main()
+{
+    cin >> n >> s;
+    len = s.size();
+    for (int i = 0; i < len; i++)
+    {
+        if (s[i] == 'x')
+        {
+            pre = i;
+            break;
+        }
+    }
+    for (char i = '0'; i <= '9'; i++)
+    {
+        s[pre] = i;
+        int ans = Get_ans(s);
+        if (ans == s[len - 1] - '0')
+        {
+            cout << i;
+            return 0;
+        }
+    }
+    return 0;
+}