poj 1724 ROADS

传送门：http://poj.org/problem?id=1724

注意有重边！

①Dijsktra+优先队列（16ms）：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;

const int INF=0x3f3f3f3f;
const int maxn=10010;
int T,n,k,r,e;
int head[maxn];

struct Edge{//链式前向星建图
	int v,w,c;
	int next;
}edge[maxn];

void init(){
	e=0;
	memset(head,-1,sizeof(head));
}

void addEdge(int u,int v,int w,int c){
	edge[e].v=v,edge[e].w=w,edge[e].c=c,edge[e].next=head[u];
	head[u]=e++;
}

struct node{
	int n;
	int dis;//表示源点到点n的最小距离
	int cost;//表示源点到点n的最小费用
	bool operator<(const node&a)const{//重载运算符
		return (a.dis<dis)||(dis==a.dis&&a.cost<cost);
	}
};

void Dijsktra(){
	priority_queue<node>Q;
	node s,e;
	s.n=1,s.dis=0,s.cost=0;//初始化
	Q.push(s);
	while(!Q.empty()){
		s=Q.top();Q.pop();
		if(s.n==n){//已经更新到最优解，返回结果
			printf("%d\n",s.dis);
			return ;
		}
		int u=s.n;
		for(int i=head[u];i!=-1;i=edge[i].next){
			e.n=edge[i].v;
			e.dis=s.dis+edge[i].w;
			e.cost=s.cost+edge[i].c;
			if(e.cost<=k){//判断所消耗费用是否满足条件
				Q.push(e);
			}
		}
	}
	printf("-1\n");//不存在最优解，输出-1
	return ;
}

int main(){
#ifndef ONLINE_JUDGE
	freopen("test.in","r",stdin);
	freopen("test.out","w",stdout);
#endif
	while(~scanf("%d%d%d",&k,&n,&r)){
		init();
		int u,v,w,c;
		while(r--){
			scanf("%d%d%d%d",&u,&v,&w,&c);
			addEdge(u,v,w,c);
		}
		Dijsktra();
	}
	return 0;
}

②Dfs（125ms）：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;

const int INF=0x3f3f3f3f;
const int maxn=10010;
int T,n,k,r;
int e,ans;
int head[maxn];
bool vis[105];

struct Edge{//链式前向星建图
	int v,w,c;
	int next;
}edge[maxn];

void init(){
	e=0;
	memset(head,-1,sizeof(head));
	memset(vis,0,sizeof(vis));
}

void addEdge(int u,int v,int w,int c){
	edge[e].v=v,edge[e].w=w,edge[e].c=c,edge[e].next=head[u];
	head[u]=e++;
}

void Dfs(int u,int dis,int cost){
	if(cost>k) return ;
	if(dis>ans) return ;
	if(u==n){
		ans=dis;
		return ;
	}
	for(int i=head[u];i!=-1;i=edge[i].next){
		int v=edge[i].v;
		if(!vis[v]){
			vis[v]=1;
			Dfs(v,dis+edge[i].w,cost+edge[i].c);
			vis[v]=0;
		}
	}
}

int main(){
#ifndef ONLINE_JUDGE
	freopen("test.in","r",stdin);
	freopen("test.out","w",stdout);
#endif
	while(~scanf("%d%d%d",&k,&n,&r)){
		init();
		int u,v,w,c;
		while(r--){
			scanf("%d%d%d%d",&u,&v,&w,&c);
			addEdge(u,v,w,c);
		}
		ans=INF;
		Dfs(1,0,0);
		if(ans==INF)
			printf("-1\n");
		else
			printf("%d\n",ans);
	}
	return 0;
}