poj 3352 Road Construction

http://poj.org/problem?id=3352

  1 #include <cstdio>

  2 #include <iostream>

  3 #include <cstring>

  4 #include <queue>

  5 #include <algorithm>

  6 #define maxn 300000

  7 using namespace std;

  8 

  9 const int inf=1<<30;

 10 int head[maxn],dfn[maxn],low[maxn],belong[maxn],stack1[maxn],du[maxn];

 11 int e,bcc_clock,bcnt,top,N,E;

 12 bool vis[maxn],visi[maxn];

 13 

 14 struct node

 15 {

 16     int u,v,next;

 17 } p[maxn];

 18 

 19 void add(int u,int v)

 20 {

 21     p[e].u=u;

 22     p[e].v=v;

 23     p[e].next=head[u];

 24     head[u]=e++;

 25     p[e].u=v;

 26     p[e].v=u;

 27     p[e].next=head[v];

 28     head[v]=e++;

 29 }

 30 

 31 void tarjan(int u,int fa)

 32 {

 33     vis[u]=true;

 34     dfn[u]=low[u]=++bcc_clock;

 35     stack1[++top]=u;

 36     for(int i=head[u]; i!=-1; i=p[i].next)

 37     {

 38         int v=p[i].v;

 39         if(v==fa) continue;

 40         if(!dfn[v])

 41         {

 42             tarjan(v,u);

 43             low[u]=min(low[u],low[v]);

 44         }

 45         else if(vis[v])

 46         {

 47             low[u]=min(low[u],dfn[v]);

 48         }

 49     }

 50     if(dfn[u]==low[u])

 51     {

 52         bcnt++;

 53         int j;

 54         do

 55         {

 56             j=stack1[top--];

 57             vis[j]=false;

 58             belong[j]=bcnt;

 59         }

 60         while(j!=u);

 61     }

 62 }

 63 

 64 void deal()

 65 {

 66     bcc_clock=0,bcnt=0,top=0;

 67     memset(vis,false,sizeof(vis));

 68     memset(belong,0,sizeof(belong));

 69     memset(dfn,0,sizeof(dfn));

 70     tarjan(1,1);

 71 }

 72 

 73 void dfs(int u)

 74 {

 75     visi[u]=true;

 76     for(int i=head[u]; i!=-1; i=p[i].next)

 77     {

 78         int v=p[i].v;

 79         if(!visi[v])

 80         {

 81             if(belong[v]!=belong[u])

 82             {

 83                 ++du[belong[u]];

 84                 ++du[belong[v]];

 85             }

 86             dfs(v);

 87         }

 88     }

 89 }

 90 void inti()

 91 {

 92     memset(head,-1,sizeof(head));

 93     e=0;

 94 }

 95 

 96 int main()

 97 {

 98     while(cin>>N>>E)

 99     {

100         inti();

101         int x,y;

102         for(int i=0; i<E; i++)

103         {

104             scanf("%d%d",&x,&y);

105             add(x,y);

106         }

107         deal();

108         if(bcnt==1)

109         {

110             printf("0\n");

111             continue;

112         }

113         memset(du,0,sizeof(du));

114         int leaf=0;

115         memset(visi,false,sizeof(visi));

116         dfs(1);

117         for(int i=1; i<=bcnt; i++)

118         {

119             if(du[i]==1) leaf++;

120         }

121         printf("%d\n",(leaf+1)/2);

122     }

123     return 0;

124 }

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