POJ_1511_Invitation Cards(最短路)

标签：acm   algorithm   poj   最短路   

Description

Input

Output

Sample Input

2
2 2
1 2 13
2 1 33
4 6
1 2 10
2 1 60
1 3 20
3 4 10
2 4 5
4 1 50

Sample Output

46
210

题意：在有向图中，求1到所有点的最短路之和 + 所有点到1的最短路之和。

分析：很明显地，利用spfa or dijkstra+heap，顺着存边求一次最短路，然后把边反向求一次最短路，然后求和即可。如果这个题目用vector存图的话，那么很容易卡时间，比如存图我用两个临接表直接存储就TLE了，后来改成一个临接表才过的。然而这样子还是卡时间，还可以继续优化。题意很清晰，边的数量是1000000，那么我们可以直接用结构体数组把边存下来，这样子在数组上操作，就不会很费时了。具体见代码：

题目链接：http://poj.org/problem?id=1511

代码清单：

vector实现（时间复杂度高）：

#include<queue>
#include<vector>
#include<stdio.h>
#include<string.h>
#include<iostream>
#include<algorithm>
using namespace std;

typedef long long ll;
const int maxn=1000000+5;
const int max_dis=1e9 + 5;

struct Edge{
    int to,dis;
    Edge(int to,int dis){
        this -> to = to;
        this -> dis = dis;
    }
};

struct edge{
    int from,to,dis;
}g[maxn];
int T;
int n,Q;
int a,b,c;
int d[maxn];
bool vis[maxn];
typedef pair<int,int>P;
vector<Edge>graph[maxn];
void Clear(){
    for(int i=1;i<=n;i++){
        graph[i].clear();
    }
}

void input(){
    scanf("%d%d",&n,&Q);
    Clear();
    for(int i=0;i<Q;i++){
        scanf("%d%d%d",&g[i].from,&g[i].to,&g[i].dis);
        graph[g[i].from].push_back(Edge(g[i].to,g[i].dis));
    }
}

ll dijkstra(){
    fill(d+1,d+1+n,max_dis);    
    priority_queue<P,vector<P>,greater<P> >q;
    while(q.size())   q.pop();
    d[1]=0;
    q.push(P(0,1));
    while(q.size()){
        P p=q.top(); q.pop();
        int v=p.second;
        if(d[v]<p.first) continue;
        for(int i=0;i<graph[v].size();i++){
            Edge& e=graph[v][i];
            if(d[e.to]>d[v]+e.dis){
                d[e.to]=d[v]+e.dis;
                q.push(P(d[e.to],e.to));
            }
        }
    }
    ll ret=0;
    for(int i=1;i<=n;i++) ret+=d[i];
    return ret;
}

ll spfa(){
    memset(vis,false,sizeof(vis));
    fill(d+1,d+1+n,max_dis);
    queue<int>q;
    while(!q.empty()) q.pop();
    d[1]=0;
    vis[1]=true;
    q.push(1);
    while(!q.empty()){
        int p=q.front(); q.pop();
        vis[p]=0;
        for(int i=0;i<graph[p].size();i++){
            Edge& e=graph[p][i];
            if(d[e.to]>d[p]+e.dis){
                d[e.to]=d[p]+e.dis;
                if(!vis[e.to]){
                    vis[e.to]=true;
                    q.push(e.to);
                }
            }
        }
    }
    ll ret=0;
    for(int i=1;i<=n;i++) ret+=d[i];
    return ret;
}

void dijkstra_solve(){
    ll ans=dijkstra();
    Clear();
    for(int i=0;i<Q;i++){
        graph[g[i].to].push_back(Edge(g[i].from,g[i].dis));
    }
    ans+=dijkstra();
    printf("%I64d\n",ans);
}

void spfa_solve(){
    ll ans=spfa();
    Clear();
    for(int i=0;i<Q;i++){
        graph[g[i].to].push_back(Edge(g[i].from,g[i].dis));
    }
    ans+=spfa();
    printf("%I64d\n",ans);
}

int main(){
    scanf("%d",&T);
    while(T--){
        input();
        dijkstra_solve();
        //spfa_solve();
    }return 0;
}

#include<queue>
#include<vector>
#include<stdio.h>
#include<string.h>
#include<iostream>
#include<algorithm>
using namespace std;

typedef long long ll;
const int maxn=1000000+5;
const int max_dis=1e9 + 5;

struct Edge{int to,dis,next;}graph[maxn];
struct edge{int from,to,dis;}g[maxn];

int T;
int n,Q;
int num;
int d[maxn];
bool vis[maxn];
int head[maxn];
typedef pair<int,int>P;

void Clear(){
    num=0;
    memset(head,-1,sizeof(head));
    memset(graph,0,sizeof(graph));
}

void add(int u,int v,int dis){
    graph[num].to=v;
    graph[num].dis=dis;
    graph[num].next=head[u];
    head[u]=num++;
}

void input(){
    scanf("%d%d",&n,&Q);
    Clear();
    for(int i=0;i<Q;i++){
        scanf("%d%d%d",&g[i].from,&g[i].to,&g[i].dis);
        add(g[i].from,g[i].to,g[i].dis);
    }
}

ll dijkstra(){
    fill(d+1,d+1+n,max_dis);
    priority_queue<P,vector<P>,greater<P> >q;
    while(q.size())   q.pop();
    d[1]=0;
    q.push(P(0,1));
    while(q.size()){
        P p=q.top(); q.pop();
        int v=p.second;
        if(d[v]<p.first) continue;
        for(int k=head[v];k>-1;k=graph[k].next){
            if(d[graph[k].to]>d[v]+graph[k].dis){
                d[graph[k].to]=d[v]+graph[k].dis;
                q.push(P(d[graph[k].to],graph[k].to));
            }
        }
    }
    ll ret=0;
    for(int i=1;i<=n;i++) ret+=d[i];
    return ret;
}

ll spfa(){
    memset(vis,false,sizeof(vis));
    fill(d+1,d+1+n,max_dis);
    queue<int>q;
    while(!q.empty()) q.pop();
    d[1]=0;
    vis[1]=true;
    q.push(1);
    while(!q.empty()){
        int v=q.front(); q.pop();
        vis[v]=0;
        for(int k=head[v];k>-1;k=graph[k].next){
            if(d[graph[k].to]>d[v]+graph[k].dis){
                d[graph[k].to]=d[v]+graph[k].dis;
                if(!vis[graph[k].to]){
                    vis[graph[k].to]=true;
                    q.push(graph[k].to);
                }
            }
        }
    }
    ll ret=0;
    for(int i=1;i<=n;i++) ret+=d[i];
    return ret;
}

void dijkstra_solve(){
    ll ans=dijkstra();
    Clear();
    for(int i=0;i<Q;i++){
        add(g[i].to,g[i].from,g[i].dis);
    }
    ans+=dijkstra();
    printf("%I64d\n",ans);
}

void spfa_solve(){
    ll ans=spfa();
    Clear();
    for(int i=0;i<Q;i++){
        add(g[i].to,g[i].from,g[i].dis);
    }
    ans+=spfa();
    printf("%I64d\n",ans);
}
int main(){
    scanf("%d",&T);
    while(T--){
        input();
        //dijkstra_solve();
        spfa_solve();
    }return 0;
}

POJ_1511_Invitation Cards(最短路)

标签：acm   algorithm   poj   最短路   

原文地址：http://blog.csdn.net/jhgkjhg_ugtdk77/article/details/47095345