桥边数量

 1 type edge=record
 2         nt,u,v:longint;
 3         end;
 4 const     maxn=100008;
 5       maxm=200008;
 6 var eg:array[0..maxm*2] of edge;
 7     lt:array[0..maxn] of longint;
 8     dfn,low,stack,cl:array[0..maxn] of longint;
 9     i,j,n,m,u,v,sum,num,k:longint;
10     tmp,now:longint;
11 procedure add(u,v:longint);
12 begin
13     inc(sum);
14     eg[sum].u:=u;
15     eg[sum].v:=v;
16     eg[sum].nt:=lt[u];
17     lt[u]:=sum;
18 end;
19 function min(a,b:longint):longint;
20 begin
21     if a<b then exit(a) else exit(b);
22 end;
23 procedure dfs(u,fa:longint);
24 var v,i:longint;
25 begin
26     inc(tmp); dfn[u]:=tmp; low[u]:=tmp;
27     inc(now); stack[now]:=u;
28     i:=lt[u];
29     while i<>-1 do
30     begin
31         v:=eg[i].v;
32         if v<>fa then
33             if dfn[v]=0 then
34             begin
35                 dfs(v,u);
36                 low[u]:=min(low[u],low[v]);
37             end
38             else low[u]:=min(low[u],dfn[v]);
39         i:=eg[i].nt;
40     end;
41     if dfn[u]=low[u] then
42     begin
43         inc(num);
44         while true do
45         begin
46             v:=stack[now];
47             cl[v]:=num;
48                         dec(now);
49             if u=v then break;
50         end;
51     end;
52 end;
53 begin
54     for i:=1 to maxn do lt[i]:=-1;
55     readln(n,m);
56     sum:=-1;
57     for i:=1 to m do
58     begin
59         readln(u,v);
60         add(u,v);
61         add(v,u);
62     end;
63     for i:=1 to n do
64         if dfn[i]=0 then
65             dfs(i,0);
66     for i:=1 to sum do
67         if odd(i) then
68         begin
69             if cl[eg[i].u]<>cl[eg[i].v] then inc(k);
70         end;
71        writeln(k);
72        //for i:=1 to n do write(cl[i],‘  ‘);
73 end.