特征距离

Posted 2020-11-02 songt

题目链接： http://exercise.acmcoder.com/online/online_judge_ques?ques_id=3347&konwledgeId=40

解题思路： 直接求出所有的最短路，以及最短路上的特征距离。

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 
 4 typedef long long LL;
 5 const int inf=0x3f3f3f3f;
 6 const int MAXN=100005;
 7 const LL MON7 = 1e9+7;
 8 
 9 struct Edge
10 {
11     int v,c;
12     Edge(){}
13     Edge(int v, int c):v(v),c(c){}
14 }edge[10*MAXN];
15 int head[MAXN];
16 int dis[MAXN];
17 int fdis[MAXN];
18 bool vis[MAXN];
19 int next_edge[10*MAXN];
20 int cnt;
21 int n,m;
22 void init()
23 {
24     memset(head,-1,sizeof(head));
25     cnt=0;
26 }
27 void addEdge(int u,int v,int c)
28 {
29     edge[cnt]=Edge(v,c);
30     next_edge[cnt]=head[u];
31     head[u]=cnt++;
32 }
33 void spfa(int s,int e)
34 {
35     for (int i=0;i<=n;++i) dis[i]=inf;
36     memset(fdis,0,sizeof(fdis));
37     dis[s]=0;
38     queue<int> q;
39     q.push(s);
40     vis[s]=1;
41     while (!q.empty())
42     {
43         int u=q.front();
44         q.pop();
45         vis[u]=0;
46         for (int i=head[u];i!=-1;i=next_edge[i])
47         {
48             int v=edge[i].v;
49             int c=edge[i].c;
50             if (dis[v]>dis[u]+c)
51             {
52                 dis[v]=dis[u]+c;
53                 fdis[v]=max(fdis[u],c);
54                 if (!vis[v]) q.push(v), vis[v]=1;
55             } else if (dis[v]==dis[u]+c && max(fdis[u],c)>fdis[v])
56             {
57                 fdis[v]=max(fdis[u],c);
58                 if (!vis[v]) q.push(v), vis[v]=1;
59             }
60         }
61     }
62     if (dis[e]==inf) printf("No answer\n");
63     else printf("%d\n",fdis[e]);
64 }
65 
66 int main()
67 {
68 #ifndef ONLINE_JUDGE
69     freopen("test.txt","r",stdin);
70 #endif // ONLINE_JUDGE
71     int Case;
72     int s,t;
73     scanf("%d",&Case);
74     for (int ct=1;ct<=Case;++ct)
75     {
76         scanf("%d%d",&n,&m);
77         scanf("%d%d",&s,&t);
78         init();
79         int u,v,c;
80         while(m--)
81         {
82             scanf("%d%d%d",&u,&v,&c);
83             addEdge(u,v,c);
84             addEdge(v,u,c);
85         }
86         printf("Case #%d: ", ct);
87         spfa(s,t);
88     }
89     return 0;
90 }