NUC_HomeWork1 -- POJ2067(最短路)

  1 /好长时间没写过最短路了，好多基础的东西都不记得了  c
  2 #include <cstdio>
  3 #include <iostream>
  4 #include <cstring>
  5 #include <cmath>
  6 #include <algorithm>
  7 #include <queue>
  8 
  9 using namespace std;
 10 
 11 
 12 const int N = 5050, INF = 10000;
 13 
 14 int head[N], nc, n; ///
 15 int dis[N];         ///计算距离的数组
 16 int stk[N], f, r;   ///用数组模拟栈，
 17 bool vis[N];        ///在用spfa时的标记数组
 18 
 19 struct Edge{        ///边
 20     int to, next, cost;
 21 }edge[100000];
 22 
 23 void add(int a, int b, int c)  ///加边函数，双向
 24 {
 25     edge[nc].to = b;
 26     edge[nc].next = head[a];
 27     edge[nc].cost = c;
 28     head[a] = nc++;
 29 
 30     edge[nc].to = a;
 31     edge[nc].next = head[b];
 32     edge[nc].cost = c;
 33     head[b] = nc++;
 34 }
 35 
 36 void fire_spfa(int fire[], int num)
 37 {
 38     memset(vis, false, sizeof(vis));
 39 
 40     f = r = 0;                      ///初始化栈
 41 
 42     for(int i = 0; i < num; i++)    ///初始化每个消防站到其他点的距离
 43     {
 44         int t = fire[i];
 45         if(!vis[t])
 46         {
 47             vis[t] = true;
 48             dis[stk[r++] = t] = 0;///初始化，并将当前点入栈
 49         }
 50     }
 51 
 52     while(f != r)               ///如果栈不为空
 53     {
 54         int now = stk[f++];     ///从栈中取出栈顶元素
 55         if(f == N) f = 0;       ///防止栈空间不够
 56 
 57         vis[now] = false;       ///将当前结点标记
 58         for(int i = head[now]; i != -1; i = edge[i].next)   ///从边表中取出元素
 59         {
 60             int to = edge[i].to;
 61             int cot = edge[i].cost;
 62 
 63             if(dis[to] > dis[now] + cot)                    ///进行松弛操作
 64             {
 65                 dis[to] = dis[now] + cot;
 66                 if(!vis[to])                                ///如果前驱没有访问过，
 67                 {
 68                     stk[r++] = to;                          ///入栈
 69                     if(r == N)
 70                         r = 0;
 71                     vis[to] = true;                         ///标记
 72                 }
 73             }
 74         }
 75     }
 76 }
 77 
 78 int spfa(int src)
 79 {
 80     memset(vis, false, sizeof(vis));
 81     f = 0;
 82     r = 1;
 83 
 84     vis[src] = true;
 85     int d[N];
 86     for(int i = 1; i <= n; ++i)     ///从当前结点到其余所有结点距离初始化
 87     {
 88         d[i] = INF;
 89     }
 90 
 91     d[src] = 0;
 92     stk[0] = src;
 93 
 94     while(f != r)
 95     {
 96         int now = stk[f++];
 97         if(f == N)
 98             f = 0;
 99         vis[now] = false;
100 
101         for(int i = head[now]; i != -1; i = edge[i].next)
102         {
103             int to = edge[i]. to;
104             int cot = edge[i].cost;
105 
106             if(d[to] > d[now] + cot)
107             {
108                 d[to] = d[now] + cot;
109                 if(!vis[to])
110                 {
111                     stk[r++] = to;
112                     vis[to] = true;
113                     if(r == N)
114                         r = 0;
115                 }
116             }
117         }
118     }
119 
120     int ans = 0;
121     for(int i = 1; i <= n; ++i)
122     {
123         ans = max(ans, min(d[i], dis[i]));
124     }
125     return ans;
126 }
127 
128 int main()
129 {
130     int ff, fire[N], a, b, c;
131 
132     memset(head, -1, sizeof(head));
133     nc = 0;
134     scanf("%d%d", &ff, &n);
135     for(int i = 0; i < ff; ++i)
136     {
137         scanf("%d", fire+i);
138     }
139 
140     while(scanf("%d%d%d", &a, &b, &c) != EOF)
141     {
142         add(a, b, c);
143     }
144 
145     for(int i = 1; i <= n; ++i)
146         dis[i] = INF;
147 
148     fire_spfa(fire, ff);
149 
150     int id = 1, ans = INF;
151 
152     for(int i = 1; i <= n; ++i)
153     {
154         if(dis[i] != 0)
155         {
156             int tp = spfa(i);
157             if(ans > tp)
158             {
159                 ans = tp;
160                 id = i;
161             }
162         }
163     }
164 
165     printf("%d\n", id);
166     return 0;
167 }