UVA 10917 Walk Through the Forest

怒刷水题。。我说怎么会TLE 原来是自己记忆化搜索写挫了。。对比才知道dijkstra比bellman跑的快好多啊。

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  1 #include <iostream>
  2 #include <cstring>
  3 #include <queue>
  4 #include <vector>
  5 #include <cstdio>
  6 #define maxn 1010
  7 using namespace std;
  8 typedef pair <int,int> pii;
  9 int d[maxn],dp[maxn],visit[maxn];
 10 int first[maxn];
 11 vector<int> st,v,w,next;
 12 int n,m,e;
 13 
 14 void init()
 15 {
 16     e = 0;
 17     st.clear();
 18     v.clear();
 19     w.clear();
 20     next.clear();
 21     memset(first,-1,sizeof(first));
 22     memset(visit,0,sizeof(visit));
 23 }
 24 void add_edge(int a,int b,int c)
 25 {
 26     //w[e] = c;
 27     w.push_back(c);
 28     //st[e] = a;
 29     st.push_back(a);
 30     //v[e] = b;
 31     v.push_back(b);
 32     //next[e] = first[a];
 33     next.push_back(first[a]);
 34     first[a] = e;
 35     e++;
 36 }
 37 void Read_Graph()
 38 {
 39     int i,j,a,b,c;
 40     e = 0;
 41     for(i = 1;i <= m;i++)
 42     {
 43         scanf("%d%d%d",&a,&b,&c);
 44         add_edge(a,b,c);
 45         add_edge(b,a,c);
 46     }
 47 }
 48 
 49 void dijkstra()
 50 {
 51     priority_queue < pii,vector<pii>,greater<pii> > q;
 52     for(int i = 0;i <= n;i++)   d[i] = 1 << 30;
 53     d[2] = 0;
 54     q.push(make_pair(0,2));
 55     while(!q.empty())
 56     {
 57         while(!q.empty() && q.top().first > d[q.top().second])   q.pop();
 58         if(q.empty())   break;
 59         int u = q.top().second;
 60         q.pop();
 61         for(int i = first[u];i != -1;i = next[i])
 62         {
 63             if(d[v[i]] > d[u] + w[i])
 64             {
 65                 d[v[i]] = d[u] + w[i];
 66                 q.push(make_pair(d[v[i]],v[i]));
 67             }
 68         }
 69     }
 70 }
 71 
 72 void Bellman_Ford()
 73 {
 74     int i,j;
 75     for(i = 1;i <= n;i++)   d[i] = 1 << 30;
 76     d[2] = 0;
 77     for(i = 1;i <= n;i++)
 78         for(j = 0;j < e;j++)
 79             d[v[j]] = d[st[j]] + w[j] < d[v[j]] ? d[st[j]] + w[j] : d[v[j]];
 80 }
 81 
 82 int DP(int u)
 83 {
 84     int &ans = dp[u];
 85     if(visit[u])    return ans;
 86     visit[u] = 1;
 87     for(int i = first[u];i != -1;i = next[i])
 88         if(d[u] < d[v[i]])
 89             ans += DP(v[i]);
 90     return ans;
 91 }
 92 
 93 void solve()
 94 {
 95     Read_Graph();
 96     dijkstra();
 97     //Bellman_Ford();
 98     int i,j;
 99     memset(dp,0,sizeof(dp));
100     dp[1] = 1;
101     printf("%d\n",DP(2));
102 }
103 
104 int main()
105 {
106     while(scanf("%d",&n),n)
107     {
108         scanf("%d",&m);
109         init();
110         solve();
111     }
112     return 0;
113 }

 

posted @ 2012-12-12 14:45  浙西贫农  阅读(342)  评论(0)  编辑  收藏  举报