【POJ1003】Hangover（二分搜索）

直接用库函数二分即可。

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <cctype>
#include <algorithm>
#include <numeric>

#define eps 1e-8
using namespace std;

double len[500];

int main () {
    ios :: sync_with_stdio(false);
    len[0] = 0;
    for (int i = 1; i < 300; ++ i) {
        len[i] = len[i - 1] + 1.0 / (double)(i + 1);
    }

    //cout << len[273] << endl;
    double n;
    while (cin >> n) {
        if (n - 0 < eps) {
            break;
        }
        //cout << lower_bound(len, len + 300, n) - &len[0] << endl;
        printf ("%d card(s)
", lower_bound(len, len + 300, n) - &len[0]);
    }
    return 0;
}