P1909 买铅笔 倍增思想

 1 #include <iostream>
 2 using namespace std;
 3 int main()
 4 {
 5     int L,ans = 0, num, price;
 6     cin>>L;  //需要买的笔的数量
 7     for(int i = 0; i < 3; i++)
 8     {
 9         cin>>num>>price;   //输入一包笔的数量， 笔的价格
10         int num1 = num, cost = price;
11         while(L > num) num <<= 1, price <<= 1;   //倍增
12         while(num > L) num -= num1, price -= cost;  //买多了
13         while(L > num) num += num1, price += cost;  //微调
14         if(ans == 0 || price < ans) ans = price;  //判断最小花费
15     }
16     cout<<ans<<endl;
17     return 0;
18 }