[最短路径] HDU 2112 - HDU Today

来源：互联网发布：网络诈骗论文2000字编辑：程序博客网时间：2024/05/17 01:10

最短路径 - Dijkstra算法。是单源点最短路径算法.

由当前最优解递推全局最优解，每次寻找距离起点权值最小的结点，进行路径更新，具体证明在这里就不写了。

本题给的每个结点是一个字符串，可以用map解决。

本题注意：

1、此图是无向图

2、结点到自己的距离是0

3、起点和终点在图中可能没有

#include <stdio.h>#include <string.h>#include <math.h>#include <stdlib.h>#include <algorithm>#include <iostream>#include <set>#include <map>#include <queue>#include <stack>#include <assert.h>#include <time.h>#define Max 160typedef long long LL;const int INF = 500000001;const double EPS = 1e-9;const double PI = acos(-1.0);using namespace std;int graph[Max][Max], s, e;int val[Max], vis[Max];void init(){    for(int i = 0; i < Max; i++)    {        for(int j = 0; j < Max; j++)        {            if(i == j)                graph[i][j] = 0;            else                graph[i][j] = INF;        }    }}void dijkstra(){    for(int i = 0; i < Max; i++)    {        val[i] = graph[s][i];        vis[i] = -1;    }    vis[s] = 1;    int minn, v;    for(int j = 1; j < Max; j++)    {        minn = INF;        v = -1;        for(int i = 0; i < Max; i++)        {            if(vis[i] == -1 && minn > val[i])            {                minn = val[i];                v = i;            }        }        if(v == -1)        {            break;        }        vis[v] = 1;        for(int i = 0; i < Max; i++)        {            if(vis[i] == -1)            {                val[i] = min(val[i], val[v] + graph[v][i]);            }        }    }}int main(){    #ifdef _1Test        freopen("test0.in", "r", stdin);        freopen("test0.out", "w", stdout);        srand(time(NULL));    #endif    int N, cnt, dis;    char ch[4][100];    while(scanf("%d", &N), N != -1)    {        map<string, int> mm;        cnt = 0;        scanf("%s %s", ch[0], ch[1]);        init();        for(int i = 0; i < N; i++)        {            scanf("%s %s %d", ch[2], ch[3], &dis);            if(mm.find(ch[2]) == mm.end())            {                mm[ch[2]] = cnt++;            }            if(mm.find(ch[3]) == mm.end())            {                mm[ch[3]] = cnt++;            }            int v1 = mm[ch[2]], v2 = mm[ch[3]];            graph[v1][v2] = graph[v2][v1] = min(dis, graph[v1][v2]);        }        if(mm.find(ch[0]) == mm.end())        {            mm[ch[0]] = cnt++;        }        if(mm.find(ch[1]) == mm.end())        {            mm[ch[1]] = cnt++;        }        s = mm[ch[0]];        e = mm[ch[1]];        dijkstra();        if(val[e] == INF)            printf("-1\n");        else            printf("%d\n", val[e]);    }    return 0;}

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