poj 2431 Expedition最优加油方法

思路: 1.让车一直走，走到没油才开始加油.

          2.开始加油加最多的油.

此问题为贪心问题。

 

代码：

#include 
#include 
#include 
#include 
#include 

bool cmp(const std::pair &a, const std::pair &b) {
	return a.first > b.first;
}

int get_minimum_stop(int L, int P, std::vector > &stop) {
	int curr_capacity = P;	// 当前油量
	int result = 0; // 加油次数
	std::priority_queue Q; // 用最大堆存储油量
	stop.push_back(std::make_pair(0, 0));
	std::sort(stop.begin(), stop.end(), cmp);

	for (int i = 0; i < stop.size(); i++) {
		int dis = L - stop[i].first;
		while (curr_capacity < dis && !Q.empty()) { // 燃料不够距离，开始加油
			curr_capacity += Q.top();
			Q.pop();
			result++;
		}
		if (Q.empty() && curr_capacity < dis) // 油加完了还不够，说明到不了
			return -1;
		curr_capacity -= dis;
		L = stop[i].first;
		Q.push(stop[i].second);
	}
	return result;
}

int main() {
	std::vector > stop;
	int N, L, P, distance, fuel;
	scanf("%d", &N);
	for (int i = 0; i < N; i++) {
		scanf("%d %d", &distance, &fuel);
		stop.push_back(std::make_pair(distance, fuel));
	}
	scanf("%d %d", &L, &P);
	printf("%d\n", get_minimum_stop(L, P, stop));
	return 0;
}