poj1040

參考：http://blog.csdn.net/dreamvyps/article/details/6069844

菜鳥，一直對DFS很困惑。。。。

測試數據：http://poj.org/showmessage?message_id=17837

不要忘了處理訂單數爲0的情況

 

//Problem: 1040 
//Memory: 224K  Time: 438MS 
//Language: C++  Result: Accepted 

#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

const unsigned MaxOrder = 22;
const unsigned MaxStop = 7;

typedef struct _ORDER
{
	int from;
	int to;
	int passengerCnt;
	int value;//該order可以得到的價值
}Order;

vector<Order> order;
int stop[MaxStop];
int capacity,station,ordernum;
int maxV;

inline bool cmp(const Order &a, const Order &b)//按照每個order的value進行降序排序
{
	return a.value>b.value;
}
void Dfs(int s, int curMaxV)
{
	if(curMaxV>maxV)
		maxV = curMaxV;
	if(s>=order.size())
		return;
	int i, j;
	for(i=s; i<order.size(); ++i)
	{
		for(j=order[i].from; j<order[i].to; ++j)
		{
			stop[j] += order[i].passengerCnt;
			if(stop[j]>capacity)
				break;
		}
		if(j==order[i].to)//還有空餘座位
		{
			Dfs(i+1,curMaxV+order[i].value);
			--j;
		}

		//回溯
		for(int k=j; k>=order[i].from; --k)
			stop[k] -= order[i].passengerCnt;
	}
}
int main()
{
	Order tmp;
	int i;

	cin>>capacity>>station>>ordernum;
	while(capacity!=0)
	{
		if(ordernum==0)//處理order爲0的情況
		{
			cout<<0<<endl;
		}
		else
		{
			memset(stop,0,sizeof(stop));
			for(i=0; i<ordernum; ++i)
			{
				cin>>tmp.from>>tmp.to>>tmp.passengerCnt;
				if(tmp.passengerCnt<=capacity)//如果單張訂單的乘客數大於容量則直接忽略該訂單
				{
					tmp.value = (tmp.to-tmp.from)*tmp.passengerCnt;
					order.push_back(tmp);
				}
			}
			sort(order.begin(),order.end(),cmp);//將所有的order按照其提供的價值進行降序排序
			maxV = 0;
			Dfs(0,0);
			cout<<maxV<<endl;
			order.clear();
		}
		cin>>capacity>>station>>ordernum;
	}
	return 0;
}