数学 Codeforces Round #219 (Div. 2) B. Making Sequences is Fun

题目传送门

 /*
     数学：这题一直WA在13组上，看了数据才知道是计算cost时超long long了
         另外不足一个区间的直接计算个数就可以了
 */
 #include <cstdio>
 #include <cmath>
 #include <iostream>
 #include <algorithm>
 #include <cstring>
 using namespace std;

 typedef unsigned long long ull;
 int get_len(ull x)
 {
     int ret = ;
     while (x) {
         x /= ;    ret++;
     }
     return ret;
 }

 int main(void)      //Codeforces Round #219 (Div. 2) B. Making Sequences is Fun
 {
     //freopen ("B.in", "r", stdin);

     ull w, m, k;
     while (cin >> w >> m >> k) {
         int len = get_len (m);   ull mx = ;
         for (int i=; i<=len; ++i) {
             mx = mx *  + ;
         }

         ull ans = ; ull cost = (mx - m + ) * k * len;
         while (cost <= w) {
             w -= cost;  ans += (mx - m + );
             len++;  m = mx + ; mx = mx *  + ;
             cost = (mx - m + ) * k * len;
         }

         ans += w / (len * k);
         cout << ans << endl;
     }

     return ;
 }

 #include <cstdio>
 #include <cmath>
 #include <iostream>
 #include <algorithm>
 #include <cstring>
 using namespace std;

 typedef long long ll;
 int get_len(ll x)
 {
     int ret = ;
     while (x) {
         x /= ;    ret++;
     }
     return ret;
 }

 int main(void)      //Codeforces Round #219 (Div. 2) B. Making Sequences is Fun
 {
     //freopen ("B.in", "r", stdin);

     ll w, m, k;
     while (scanf ("%I64d%I64d%I64d", &w, &m, &k) == ) {
         int len = get_len (m);   ll mx = ;
         for (int i=; i<=len; ++i) {
             mx = mx *  + ;
         }

         ll ans = , now = , tot = ;
         while (true) {
             now = mx - m + ;   tot = w / (k * len);
             if (now < tot) {
                 ans += now; w -= now * k * len;
                 m = mx + ; mx = mx *  + ;   len++;
             }
             else {
                 ans += tot; break;
             }
         }

         printf ("%I64d\n", ans);
     }

     return ;
 }

按个数比较