Codeforces Round #540 A. Water Buying
Polycarp wants to cook a soup. To do it, he needs to buy exactly n liters of water.
There are only two types of water bottles in the nearby shop — 1-liter bottles and 2-liter bottles. There are infinitely many bottles of these two types in the shop.
The bottle of the first type costs aa burles and the bottle of the second type costs bb burles correspondingly.
Polycarp wants to spend as few money as possible. Your task is to find the minimum amount of money (in burles) Polycarp needs to buy exactly nn liters of water in the nearby shop if the bottle of the first type costs a burles and the bottle of the second type costs b burles.
You also have to answer q independent queries.
The first line of the input contains one integer q (1≤q≤500) — the number of queries.
The next n lines contain queries. The i-th query is given as three space-separated integers ni, ai and bi (1≤ni≤1012,1≤ai,bi≤1000) — how many liters Polycarp needs in the i-th query, the cost (in burles) of the bottle of the first type in the ii-th query and the cost (in burles) of the bottle of the second type in the i-th query, respectively.
Print q integers. The i-th integer should be equal to the minimum amount of money (in burles) Polycarp needs to buy exactly ni liters of water in the nearby shop if the bottle of the first type costs ai burles and the bottle of the second type costs bi burles.
4 10 1 3 7 3 2 1 1000 1 1000000000000 42 88
10 9 1000 42000000000000
思路:
我们选择购买的方式受到三个因素影响:
- 瓶子容积(已知因素)
- 瓶子价格
- 需求量
在输入中给出需求量和需求量之后,首先我们需要考虑瓶子在此价格下装同体积水,哪种类型更加划算。也就是:
a/1 > b/2 ? b价格瓶划算 : a价格瓶划算;
之后,我们用划算的瓶子尽量装水,满足需求量(1L的直接全部用a价格瓶子,2L的最后可能会剩下1L,这时使用a价格的瓶子装。)
#include <iostream> using namespace std; int main() { int q; cin >> q; while (q--) { long long ni, ai, bi, min; cin >> ni >> ai >> bi; if (ai * 2 < bi) { min = ni * ai; } else { min = (ni / 2) * bi + (ni % 2) * ai; } cout << min << endl; } return 0; }

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