hdu 4823 Energy Conversion(数学)

题目链接：hdu 4823 Energy Conversion

题目大意：中文题，不解释。

解题思路：首先判断一下m是否已经大于n了，如果大于那么就是0，假设中间变换的各个值为ai，那么bi=ai+c，bi数组为等比数组（可推），所以就有了cnt=log((n+c)a)log(double(k)),结果为浮点数，需要向上取整。

#include <cstdio>#include <cstring>#include <cmath>int main () {    int cas;    double n, m, v, k;    scanf("%d", &cas);    while (cas--) {        scanf("%lf%lf%lf%lf", &n, &m, &v, &k);        if (m >= n) {            printf("0\n");            continue;        }        double tmp = (m-v)*k;        if (tmp <= m) {            printf("-1\n");        } else {            double c = -(v * k) / (k - 1);            double a = m + c;            double cnt = log((n+c) / a) / log(double(k));            printf("%lld\n", (long long)ceil(cnt));        }    }    return 0;}