HDU 4738 Caocao's Bridges(Tarjan)

题目链接

  1 #include <iostream>

  2 #include <cstring>

  3 #include <cstdio>

  4 #include <queue>

  5 #include <cstdlib>

  6 using namespace std;

  7 #define N 1001

  8 #define M 20000001

  9 #define INF 0x3f3f3f3f

 10 struct node

 11 {

 12     int u,v,next;

 13 }edge[M];

 14 int first[N],DFN[N],Belong[N],stack[N],Low[N],cnum[N];

 15 int in[N],d[N];

 16 int qu[M],qv[M],qw[M];

 17 int n,m;

 18 bool vis[M];

 19 int tot,scnt,top;

 20 int o[M];

 21 void CL()

 22 {

 23     tot = scnt = top = 0;

 24     memset(first,-1,sizeof(first));

 25     memset(in,0,sizeof(in));

 26     memset(DFN,0,sizeof(DFN));

 27     memset(vis,0,sizeof(vis));

 28 }

 29 void add(int u,int v,int w)

 30 {

 31     edge[tot].u = u;

 32     edge[tot].v = v;

 33     edge[tot].next = first[u];

 34     first[u] = tot ++;

 35 }

 36 void Tarjan(int u)

 37 {

 38     int v,i;

 39     DFN[u] = Low[u] = ++ tot;

 40     stack[top++] = u;

 41     in[u] = 1;

 42     for(i = first[u];i != -1;i = edge[i].next)

 43     {

 44         v = edge[i].v;

 45         if(vis[i]) continue;

 46         vis[i] = vis[i^1] = 1;

 47         if(!DFN[v])

 48         {

 49             Tarjan(v);

 50             Low[u] = min(Low[u],Low[v]);

 51         }

 52         else

 53         {

 54             Low[u] = min(Low[u],DFN[v]);

 55         }

 56     }

 57     if(DFN[u] == Low[u])

 58     {

 59         scnt ++;

 60         do

 61         {

 62             v = stack[--top];

 63             Belong[v] = scnt;

 64             in[v] = 0;

 65             cnum[scnt] ++;

 66         }while(u != v);

 67     }

 68 }

 69 int find(int x)

 70 {

 71     int r,t;

 72     r = x;

 73     while(o[x] != x)

 74     x = o[x];

 75     while(r != x)

 76     {

 77         t = o[r];

 78         o[r] = x;

 79         r = t;

 80     }

 81     return x;

 82 }

 83 void merge(int x,int y)

 84 {

 85     x = find(x);

 86     y = find(y);

 87     if(x != y)

 88     o[x] = y;

 89 }

 90 int main()

 91 {

 92     int n,m,i,u,v,w,minz;

 93     while(scanf("%d%d",&n,&m)!=EOF)

 94     {

 95         if(n == 0&&m == 0) break;

 96         CL();

 97         for(i = 1;i <= n;i ++)

 98         {

 99             o[i] = i;

100         }

101         for(i = 0;i < m;i ++)

102         {

103             scanf("%d%d%d",&u,&v,&w);

104             qu[i] = u;

105             qv[i] = v;

106             qw[i] = w;

107             merge(u,v);

108             add(u,v,w);

109             add(v,u,w);

110         }

111         int fa = find(1);

112         for(i = 2;i <= n;i ++)

113         {

114             if(find(i) != fa)

115             break;

116         }

117         if(i != n+1)

118         {

119             printf("0\n");

120             continue;

121         }

122         minz = 10000000;

123         Tarjan(1);

124         for(i = 0;i < m;i ++)

125         {

126             if(Belong[qu[i]] != Belong[qv[i]])

127             {

128                 minz = min(minz,qw[i]);

129             }

130         }

131         if(scnt == 1)

132         printf("-1\n");

133         else

134         {

135             if(minz == 0)

136             printf("1\n");

137             else

138             printf("%d\n",minz);

139         }

140     }

141 

142 }