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 = 0;
    while (x) {
        x /= 10;    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 = 0;
        for (int i=1; i<=len; ++i) {
            mx = mx * 10 + 9;
        }

        ull ans = 0; ull cost = (mx - m + 1) * k * len;
        while (cost <= w) { 
            w -= cost;  ans += (mx - m + 1);
            len++;  m = mx + 1; mx = mx * 10 + 9;
            cost = (mx - m + 1) * k * len;
        }
        
        ans += w / (len * k);
        cout << ans << endl;
    }

    return 0;
}

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

typedef long long ll;
int get_len(ll x)
{
    int ret = 0;
    while (x) {
        x /= 10;    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) == 3) {
        int len = get_len (m);   ll mx = 0;
        for (int i=1; i<=len; ++i) {
            mx = mx * 10 + 9;
        }

        ll ans = 0, now = 0, tot = 0;
        while (true) {
            now = mx - m + 1;   tot = w / (k * len);
            if (now < tot) {
                ans += now; w -= now * k * len;
                m = mx + 1; mx = mx * 10 + 9;   len++;
            }
            else {
                ans += tot; break;
            }
        }
        
        printf ("%I64d
", ans);
    }

    return 0;
}