poj 1797 Heavy Transportation 【最短路Dijkstra 变式】

标签：最短路   dijkstra   poj   

Description

Input

Output

Sample Input

1
3 3
1 2 3
1 3 4
2 3 5

Sample Output

Scenario #1:
4

题意&分析：水题一枚，给定N个点，M条路，求从1到N的最大的最小边权，如果数据在300以内，Floyd水过，但是这个题不行，N<1000，那么，我们就可以用Dijstra来做，这里需要注意的应该就是 初始化以及顶点的松弛操作：

d[y] = max(d[y], min(d[x], Map[x][y]));

网上有给最大生成树来做，也很简单，最小生成树会的话，这个也就不再话下。

下面给出两种风格的Dij代码：

/****************************>>>>HEADFILES<<<<****************************/
#include <cmath>
#include <queue>
#include <vector>
#include <cstdio>
#include <string>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <algorithm>
using namespace std;
/****************************>>>>>DEFINE<<<<<*****************************/
//#pragma comment(linker, "/STACK:1024000000,1024000000")
#define FIN             freopen("input.txt","r",stdin)
#define rep(i,a,b)      for(int i = a;i <= b;i++)
#define MP(a,b)         make_pair(a,b)
#define PB(a)           push_back(a)
#define fst             first
#define snd             second
/****************************>>>>>>DEBUG<<<<<<****************************/
#define out(x)          cout<<x<<"  ";
/****************************>>>>SEPARATOR<<<<****************************/
const int maxn = 1000 + 5;
const int INF = 0x3f3f3f3f;
int N, M, Map[maxn][maxn], d[maxn];
bool vis[maxn];
void init()
{
    memset(Map, 0, sizeof(Map));
}
void Dijkstra()
{
    memset(vis, false, sizeof(vis));
    d[1] = 0;
    rep(i,2,N) d[i] = Map[1][i];
    rep(i, 1, N-1)
    {
        int x = 0, m = 0;
        rep(y, 1, N) if(!vis[y] && d[y] > m) m = d[x = y];
        vis[x] = true;
        rep(y, 1, N)
        {
            if(!Map[x][y]) continue;
            d[y] = max(d[y], min(d[x], Map[x][y]));
        }
    }
}
int main()
{
   // FIN;
    int T, cas = 0, x, y, t;
    for(scanf("%d", &T); T--;)
    {
        scanf("%d %d", &N, &M);
        init();
        rep(i, 1, M)
        {
            scanf("%d %d %d", &x, &y, &t);
            Map[x][y] = Map[y][x] = t;
        }
        Dijkstra();
        if(cas) puts("");
        printf("Scenario #%d:\n", ++cas);
        printf("%d\n", d[N]);
    }
    return 0;
}

/****************************>>>>HEADFILES<<<<****************************/
#include <cmath>
#include <queue>
#include <vector>
#include <cstdio>
#include <string>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <algorithm>
using namespace std;
/****************************>>>>>DEFINE<<<<<*****************************/
//#pragma comment(linker, "/STACK:1024000000,1024000000")
#define FIN             freopen("input.txt","r",stdin)
#define rep(i,a,b)      for(int i = a;i <= b;i++)
#define rep0(i,b)       for(int i = 0;i < b;i++)
#define rep1(i,b)       for(int i = 1;i <= b;i++)
#define MP(a,b)         make_pair(a,b)
#define PB(a)           push_back(a)
#define fst             first
#define snd             second
/****************************>>>>>>DEBUG<<<<<<****************************/
#define out(x)          cout<<x<<"  ";
/****************************>>>>SEPARATOR<<<<****************************/
const int maxn = 1000 + 5;
const int INF = 0x3f3f3f3f;
int N,M;
struct Edge
{
    int from, to, dist;
    Edge() {}
    Edge(int _from, int _to, int _dist) : from(_from), to(_to), dist(_dist) {}
};
struct HeapNode
{
    int pos, d;
    HeapNode() {}
    HeapNode(int _pos, int _d) : pos(_pos), d(_d) {}
    bool operator < (const HeapNode & p) const
    {
        return d < p.d;
    }
};
struct Dijkstra
{
    int n, s, d[maxn];
    bool vis[maxn];
    vector<Edge> edges;
    vector<int> G[maxn];
    Dijkstra() {}
    Dijkstra(int _n, int _s) : n(_n), s(_s) {}
    void init(int _n, int _s)
    {
        this->n = _n, this->s = _s;
        edges.clear();
        rep1(i, n)
        {
            G[i].clear();
        }
    }
    void AddEdge(int u, int v, int t)
    {
        edges.PB(Edge(u, v, t));
        int m = edges.size();
        G[u].PB(m - 1);
    }
    void dijkstra()
    {
        memset(vis, false, sizeof(vis));
        memset(d,0,sizeof(d));
        d[s] = INF;
        priority_queue<HeapNode> Que;
        Que.push(HeapNode(s, 0));
        while(!Que.empty())
        {
            HeapNode now = Que.top();
            Que.pop();
            int u = now.pos;
            if(vis[u]) continue;
            vis[u] = true;

            for(int i = 0; i < G[u].size(); i++)
            {
                Edge& e = edges[G[u][i]];
                if(d[e.to] < min(d[u], e.dist))
                {
                    d[e.to] = min(d[u], e.dist);
                    Que.push(HeapNode(e.to,d[e.to]));
                }
            }
        }
    }
}dij;

int main()
{
  //  FIN;
    int T,cas = 0,x,y,t;
    for(scanf("%d",&T);T--;)
    {
        scanf("%d %d",&N,&M);
        dij.init(N,1);
        rep(i,1,M)
        {
            scanf("%d %d %d",&x,&y,&t);
            dij.AddEdge(x,y,t);
            dij.AddEdge(y,x,t);
        }
        dij.dijkstra();
        if(cas) puts("");
        printf("Scenario #%d:\n",++cas);
        printf("%d\n",dij.d[N]);
    }
    return 0;
}

poj 1797 Heavy Transportation 【最短路Dijkstra 变式】

标签：最短路   dijkstra   poj   

原文地址：http://blog.csdn.net/acmore_xiong/article/details/47291061