（连通图）Network--POJ--3694

链接：

http://acm.hust.edu.cn/vjudge/contest/view.action?cid=82833#problem/D

这部分学的不是很好，还需要努力！

代码：

  1 #include<cstdio>
  2 #include<cstdlib>
  3 #include<cmath>
  4 #include<iostream>
  5 #include<algorithm>
  6 #include<cstring>
  7 #include<vector>
  8 using namespace std;
  9 #define N 100005
 10 
 11 struct Edage{int v, next, used;} e[N<<2];
 12 
 13 int low[N], dfn[N], Head[N], fa[N], Time, cnt;
 14 int IsBridge[N], nbridge;
 15 
 16 void Init(int n)
 17 {
 18     nbridge = Time = cnt = 0;
 19 
 20     for(int i=0; i<=n; i++)
 21     {
 22         Head[i] = -1;
 23         dfn[i] = 0;
 24         IsBridge[i] = 0;
 25     }
 26 }
 27 void Add(int u, int v)
 28 {
 29     e[cnt].v = v;
 30     e[cnt].next = Head[u];
 31     e[cnt].used = false;
 32     Head[u] = cnt++;
 33 }
 34 void Tarjan(int u, int father)
 35 {
 36     int v;
 37 
 38     fa[u] = father;
 39     low[u] = dfn[u] = ++Time;
 40 
 41     for(int j=Head[u]; j!=-1; j=e[j].next)
 42     {
 43         if(!e[j].used)
 44         {
 45             e[j].used = e[j^1].used = true;
 46             v = e[j].v;
 47             if(!dfn[v])
 48             {
 49                 Tarjan(v, u);
 50                 low[u] = min(low[u], low[v]);
 51 
 52                 if(low[v]>dfn[u])
 53                 {
 54                     IsBridge[v] = true;
 55                     nbridge++;
 56                 }
 57             }
 58             else
 59                 low[u] = min(low[u], dfn[v]);
 60         }
 61     }
 62 }
 63 void LCA(int u, int v)
 64 {
 65     if(dfn[u]<dfn[v])
 66         swap(u, v);
 67 
 68     while(dfn[u] > dfn[v])
 69     {
 70         if(IsBridge[u]) nbridge--;
 71         IsBridge[u] = false;
 72         u = fa[u];
 73     }
 74 
 75     while(u!=v)
 76     {
 77         if(IsBridge[u]) nbridge--;
 78         if(IsBridge[v]) nbridge--;
 79         IsBridge[u] = IsBridge[v] = false;
 80         u = fa[u], v = fa[v];
 81     }
 82 }
 83 
 84 int main()
 85 {
 86     int n, m, k=1;
 87     while(scanf("%d%d", &n, &m), n+m)
 88     {
 89         int i, u, v;
 90 
 91         Init(n);
 92         for(i=0; i<m; i++)
 93         {
 94             scanf("%d%d", &u, &v);
 95             Add(u, v);
 96             Add(v, u);
 97         }
 98 
 99         Tarjan(1, 1);
100 
101         printf("Case %d:
", k++);
102         scanf("%d", &m);
103         for(i=0; i<m; i++)
104         {
105             scanf("%d%d", &u, &v);
106             LCA(u, v);
107             printf("%d
", nbridge);
108         }
109         printf("
");
110     }
111     return 0;
112 }

代码：

  1 #include <iostream>
  2 #include <cstdlib>
  3 #include <cstdio>
  4 #include <algorithm>
  5 #include <vector>
  6 #include <queue>
  7 #include <cmath>
  8 #include <stack>
  9 #include <cstring>
 10 usingnamespace std;
 11 #define INF 0xfffffff
 12 #define min(a,b) (a<b?a:b)
 13 #define maxn 100005
 14 int m, n, Time, ans;
 15 int dfn[maxn], low[maxn], Father[maxn], bridge[maxn];
 16 vector<int> G[maxn];
 17 
 18 void init()
 19 {
 20     memset(dfn, 0, sizeof(dfn));
 21     memset(low, 0, sizeof(low));
 22     memset(bridge, 0, sizeof(bridge));
 23     memset(Father, 0, sizeof(Father));
 24     Time = ans = 0;
 25 
 26     for(int i=0; i<=n; i++)
 27         G[i].clear();
 28 }
 29 
 30 void Tarjan(int u,int fa)
 31 {
 32     dfn[u] = low[u] = ++Time;
 33     Father[u] = fa;
 34     int len = G[u].size(), v;
 35 
 36     for(int i=0; i<len; i++)
 37     {
 38         v = G[u][i];
 39 
 40         if( !low[v] )
 41         {
 42             Tarjan(v, u);
 43             low[u] = min(low[u], low[v]);
 44 
 45             if(dfn[u] < low[v])
 46             {
 47                 bridge[v] ++;
 48                 ans ++;
 49             }
 50         }
 51         elseif(v != fa)
 52         {
 53             low[u] = min(low[u], dfn[v]);
 54 
 55             if(dfn[u] < low[v])
 56             {
 57                 bridge[v] ++;
 58                 ans --;
 59             }
 60         }
 61 
 62     }
 63 }
 64 void Lca(int a,int b)
 65 {
 66     if(a == b)
 67         return ;
 68 
 69     if(dfn[a] > dfn[b])
 70     {
 71         if( bridge[a] == 1)
 72         {
 73             bridge[a] = 0;
 74             ans --;
 75         }
 76         Lca(Father[a], b);
 77     }
 78     else
 79     {
 80         if(bridge[b] == 1)
 81         {
 82             bridge[b] = 0;
 83             ans --;
 84         }
 85         Lca(a, Father[b]);
 86     }
 87 }
 88 
 89 int main()
 90 {
 91     int cas = 1;
 92     while(scanf("%d %d",&n, &m), m+n)
 93     {
 94         int Q, a, b;
 95         init();
 96         while(m --)
 97         {
 98             scanf("%d %d",&a, &b);
 99             G[a].push_back(b);
100             G[b].push_back(a);
101         }
102 
103         scanf("%d", &Q);
104         Tarjan(1, 0);
105     //    printf("%d
", ans);
106         printf("Case %d:
", cas ++);
107         while(Q --)
108         {
109             scanf("%d %d",&a, &b);
110             Lca(a, b);
111             printf("%d
", ans);
112         }
113     }
114     return0;
115 }
116 /*
117 
118 4 4
119 1 2
120 2 1
121 2 3
122 1 4
123 2
124 1 2
125 3 4
126 
127   */

勿忘初心