1018. Public Bike Management 解析

单用Dijstra算法比较难维护。用Dijstra+DFS能简化不少。

看到有小伙伴例7有问题，可以看下是不是Dijstra的算法在计算路径的时候出问题没。我的就是下标u和i弄混了。查了好久。。。。。

#include 
#include 
#include 
#include 
#include 

using namespace std;

struct Node {
	int length;
	int Num;
};

struct Grap {
	int bIkeNum;
	vector  link;
};

void Dijkstra(Grap * g, int * dis ,vector * pre ,int N,bool * isvisit ) {
	dis[0] = 0;
	for (int i = 0; i < N; i++) {
		int u = -1, Min = INT_MAX;
		for (int j = 0; j < N; j++) { //找Dis最小值
			if (!isvisit[j] && dis[j] < Min) {
				u = j;
				Min = dis[j];
			}
		}
		if (u == -1) return;
		isvisit[u] = true;		
		for (int j = 0; j < g[u].link.size(); j++) {
			int v = g[u].link[j].Num;
			if (!isvisit[v]) {
				if (dis[u] + g[u].link[j].length < dis[v]) {//u是中间结点
					pre[v].clear();
					pre[v].push_back(u);
					dis[v] = dis[u] + g[u].link[j].length;
				}
				else if (dis[u] + g[i].link[j].length == dis[v]) {
					pre[v].push_back(u);
				}
			}
		}
	}
}





void DFS(vector  * pre, vector  & patch, vector  & tempatch, Grap * g, int & BikeNeed, int & BikeReturn, int v, int Cmax) {

	//cout << " v = " << v << endl;
	int perfect = Cmax / 2;

	if (v == 0) {
		tempatch.push_back(v);
		int bn = 0, br = 0;


		//计算大小
		//cout << "size: " << tempatch.size() << endl;
		for (int i = tempatch.size() - 1; i >= 0; i--) {
			int b = g[tempatch[i]].bIkeNum;
			if (b > perfect) {//大于perfect需要带走
				br += b - perfect;
			}
			else if (b < perfect){ //补齐
				br -= (perfect - b);
	//			cout << "br : " << br <<  endl;
				if (br < 0) {//不够补齐 要从中心调
					bn += (-br);
					br = 0;
				}
			}
		}

		//判断
		if (bn < BikeNeed) {
			BikeNeed = bn;
			BikeReturn = br;
			patch = tempatch;
		}
		else if (bn == BikeNeed && br < BikeReturn) {
			BikeNeed = bn;
			BikeReturn = br;
			patch = tempatch;
		}
		tempatch.pop_back();
		
		return;
	}
	tempatch.push_back(v);
	for (int i = 0; i < pre[v].size(); i++) {
		DFS(pre, patch, tempatch, g, BikeNeed, BikeReturn, pre[v][i], Cmax);
	}
	tempatch.pop_back();

}

int main() {

	int Cmax, N, SP, M;
	//Cmax最大容量，N站总数，SP问题站编号，M道路总数

	cin >> Cmax >> N >> SP >> M;

	Grap * g = new Grap[N + 1];
	stack  s;

	for (int i = 1; i <= N; i++) {
		cin >> g[i].bIkeNum;
	}

	g[0].bIkeNum = Cmax / 2;
	Node tempNode;
	int tempHead, tempTail;
	for (int i = 0; i < M; i++) {
		cin >> tempHead >> tempTail >> tempNode.length;
		tempNode.Num = tempTail;
		g[tempHead].link.push_back(tempNode);
		//cout << tempHead << " " << tempNode.Num << " " << tempNode.length << endl;
		tempNode.Num = tempHead;
		g[tempTail].link.push_back(tempNode);
		//cout << tempTail << " " << tempNode.Num << " " << tempNode.length << endl;
	}


//	int MinLegnth = INT_MAX;
	bool * isVisit = new bool[N + 1];
	int * dis = new int[N + 1];
	vector  * pre = new vector[N + 1];

	for (int i = 0; i <= N; i++) {
		dis[i] = INT_MAX;
		isVisit[i] = false;
	}

	Dijkstra(g, dis, pre, N + 1, isVisit);
	int BikeNeed = INT_MAX, BikeReturn = INT_MAX;


	vector  patch, tempatch;
	DFS(pre, patch, tempatch, g, BikeNeed, BikeReturn, SP, Cmax);

	cout << BikeNeed << " ";
	for (int i = patch.size() - 1; i > 0; i--) {
		cout << patch[i] << "->";
	}
	cout << patch[0] << " ";

	cout << BikeReturn << endl;
	system("pause");

 	return 0;
}