PAT A1018

题目：https://pintia.cn/problem-sets/994805342720868352/problems/994805489282433024

我用的是Dijkstra+DFS，Dijkstra问题不大，问题出在DFS中，我没有注意到题中，回来的时候不能补齐车，所以我用的“sum”就错了。要像“油箱”题一样计算。还要注意有些循环中端点是1，以及初始化的位置。

#include <cstdio>
#include <algorithm>
#include <vector>
using namespace std;
const int INF = 1e9;
const int maxn = 510;
int G[maxn][maxn], d[maxn], w[maxn] = {0}, sum = 0, back;
int c, n, sp, m;
bool vis[maxn] = {false};
vector<int> temp, path, pre[maxn];
void Dijkstra(){
	d[0] = 0;
	for(int i = 0; i <= n; i++){
		int u = -1, MIN = INF;
		for(int j = 0; j <= n; j++){
			if(!vis[j] && d[j] < MIN){
				MIN = d[j];
				u = j;
			}
		}
		if (u == -1)
			return;
		vis[u] = true;
		for(int v = 1; v <= n; v++){
			if(!vis[v] && G[u][v] != INF){
				if(d[u] + G[u][v] < d[v]){
					d[v] = d[u] + G[u][v];
					pre[v].clear();
					pre[v].push_back(u);
				}
				else if(d[u] + G[u][v] == d[v]){
					pre[v].push_back(u);
				}
			}
		}
	}
}
int minNeed = INF, minRemain = INF;
void DFS(int v){
	temp.push_back(v);
	if(!v){
		int remain = 0, need = 0;
		for(int i = temp.size() - 2 ; i >= 0; i--){
			int u = temp[i];
			if(w[u] >= 0){
				remain += w[u];
			}
			else{
				if(remain >= -w[u])
					remain += w[u];
				else{
					need += -w[u] - remain;
					remain = 0;
				}
			}
		}
		if(need < minNeed){
			minNeed = need;
			minRemain = remain;
			path = temp;
		}
		else if(need == minNeed){
			if(remain < minRemain){
				minNeed = need;
				minRemain = remain;
				path = temp;
			}
		}
		return;
	}
	for(int i = 0; i < pre[v].size(); i++){
		DFS(pre[v][i]);
		temp.pop_back();
	}
}
int main(){
	scanf("%d%d%d%d", &c, &n, &sp, &m);
	fill(w+1, w + maxn, -c/2);
	for(int i = 1; i <= n; i++){
		int weight;
		scanf("%d", &weight);
		w[i] += weight;
	}
	fill(G[0], G[0] + maxn * maxn, INF);
	for(int i = 0; i < m; i++){
		int a, b, t;
		scanf("%d%d%d", &a, &b, &t);
		G[a][b] = t;
		G[b][a] = t;
	}
	fill(d, d + maxn, INF);
	Dijkstra();
	DFS(sp);
	printf("%d ", minNeed);
	for(int i = path.size() - 1; i >= 0; i--){
		printf("%d",path[i]);
		if(i){
			printf("->");
		}
	}
	printf(" %d", minRemain);
	return 0;
}