146 lines
4.6 KiB
C++
146 lines
4.6 KiB
C++
#include<iostream>
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#include<cstring>
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#include<algorithm>
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#include<cassert>
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#include<string>
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#include<cstdio>
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#include<queue>
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#define unlikely(x) __builtin_expect(!!(x), 0)
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struct char_reader
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{
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FILE* f; char *buf,*p1,*p2; int size;
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char_reader(FILE* fin,int bufsize=1<<16) { f=fin; size=bufsize; p1=p2=0; buf=new char[size]; }
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~char_reader() { delete []buf; }
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inline int operator()() { return p1==p2&&(p2=(p1=buf)+fread(buf,1,size,f),p1==p2)?EOF:*p1++; }
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};
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struct char_writer
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{
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FILE* f; char *buf,*p,*end; int size;
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char_writer(FILE* fout,int bufsize=1<<16) { f=fout; size=bufsize; buf=new char[size]; p=buf; end=buf+bufsize; }
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~char_writer() { fwrite(buf,p-buf,1,f); delete []buf; }
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inline char operator()(char ch)
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{
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if(unlikely(end==p)) { fwrite(buf,end-buf,1,f); p=buf; }
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return *p++=ch;
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}
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};
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char_reader gch(stdin);
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char_writer wch(stdout);
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template<typename T> inline int read(T& t)
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{
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bool f=false; int ch; while(ch=gch(),!((ch>='0'&&ch<='9')||ch=='-')) { if(ch==EOF) return 0; }
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t=0;
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if(ch=='-') f=true,ch=gch(); t=ch^48; while(ch=gch(),ch>='0'&&ch<='9') t=(t<<3)+(t<<1)+(ch^48);
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if(f) t=-t;
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return 1;
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}
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inline int read(char &c)
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{
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c=0; int ch; while(ch=gch(),(ch==' '||ch=='\n'||ch=='\r'||ch=='\t')) { if(ch==EOF) return 0; } c=ch;
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return 1;
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}
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inline int read(char *s)
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{
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int ch; while(ch=gch(),(ch==' '||ch=='\n'||ch=='\r'||ch=='\t')) { if(ch==EOF) return 0; }
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*s++=ch; while(ch=gch(),!(ch==' '||ch=='\n'||ch=='\r'||ch=='\t')&&ch!=EOF) *s++=ch;
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return 1;
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} inline int read(const char *s) { return read((char*)s); }
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inline int readline(char *s)
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{
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int ch; while(ch=gch(),(ch==' '||ch=='\n'||ch=='\r'||ch=='\t')) { if(ch==EOF) return 0; }
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*s++=ch; while(ch=gch(),!(ch=='\n'||ch=='\r')&&ch!=EOF) *s++=ch;
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return 1;
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} inline int readline(const char *s) { return readline((char*)s); }
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template<typename T> inline void write(T t)
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{
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int stk[20],cnt=0;
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if(t==0) { wch('0'); return; } if(t<0) { wch('-'); t=-t; }
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while(t>0) { stk[cnt++]=t%10; t/=10; } while(cnt) wch(stk[--cnt]+'0');
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}
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inline void write(char t) { wch(t); }
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inline void write(char *s) { while(*s) wch(*s++); } inline void write(const char *s) { write((char*)s); }
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#if __cplusplus >= 201103L
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template<typename T,typename... Args> inline int read(T& t,Args&... args) { return read(t)+read(args...); }
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template<typename T,typename... Args> inline void write(T t,Args... args) { write(t); write(args...); }
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#else
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template<typename A_t,typename B_t> inline int read(A_t &a,B_t &b) { return read(a)+read(b); }
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template<typename A_t,typename B_t,typename C_t> inline int read(A_t &a,B_t &b,C_t &c) { return read(a)+read(b)+read(c); }
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template<typename A_t,typename B_t,typename C_t,typename D_t> inline int read(A_t &a,B_t &b,C_t &c,D_t &d) { return read(a)+read(b)+read(c)+read(d); }
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template<typename A_t,typename B_t> inline void write(A_t a,B_t b) { write(a); write(b); }
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template<typename A_t,typename B_t,typename C_t> inline void write(A_t a,B_t b,C_t c) { write(a); write(b); write(c); }
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template<typename A_t,typename B_t,typename C_t,typename D_t> inline void write(A_t a,B_t b,C_t c,D_t d) { write(a); write(b); write(c); write(d); }
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#endif
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using namespace std;
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typedef long long LL;
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const int maxn=5e6+10;
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const int inf=0x3f3f3f3f;
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struct Edge
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{
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int v;
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bool deleteable;
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Edge *nxt;
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}buf[maxn*2],*G[maxn],*ecnt=buf;
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inline void AddEdge(int u,int v)
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{
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ecnt->v=v;
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ecnt->nxt=G[u];
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ecnt->deleteable=false;
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G[u]=ecnt++;
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}
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int n,m,dist[maxn];
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int main()
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{
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#ifdef local
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freopen("pro.in", "r", stdin);
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// freopen("pro.out","w",stdout);
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#endif
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read(n,m);
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for(int i=0;i<m;i++)
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{
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int a,b; read(a,b);
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AddEdge(a,b);
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AddEdge(b,a);
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}
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for(int i=1;i<=n;i++) dist[i]=inf;
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dist[1]=0;
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queue<int> Q;
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Q.push(1);
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while(Q.size())
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{
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int u=Q.front(); Q.pop();
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for(Edge *it=G[u];it;it=it->nxt)
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if(dist[u]+1<dist[it->v])
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{
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dist[it->v]=dist[u]+1;
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Q.push(it->v);
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}
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}
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// for(int i=1;i<=n;i++) write("dist ",i," ",dist[i],"\n");
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for(int u=1;u<=n;u++)
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{
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int forward_cnt=0;
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bool have_parallel=false;
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for(Edge *it=G[u];it;it=it->nxt)
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{
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if(dist[u]==dist[it->v]) have_parallel=true;
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if(dist[u]==dist[it->v]+1) forward_cnt++;
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assert(abs(dist[it->v]-dist[u])<=1);
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}
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if(have_parallel||forward_cnt>=2)
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{
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// write(u," ok!\n");
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for(Edge *it=G[u];it;it=it->nxt)
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{
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if(dist[u]==dist[it->v]||dist[u]==dist[it->v]+1)
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{
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it->deleteable=true;
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buf[(it-buf)^1].deleteable=true;
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}
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}
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}
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}
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int res=0;
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for(int i=0;i<m*2;i++) res+=buf[i].deleteable;
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write(res/2,'\n');
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return 0;
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} |