题目：http://www.lydsy.com/JudgeOnline/problem.php?id=1006
题解：这题应该是留的最久的一个坑了吧。。。今天终于A掉了。。。但还是没有完全理解的感觉。
代码：
1 #include<cstdio> 2 #include<cstdlib> 3 #include<cmath> 4 #include<cstring> 5 #include<algorithm> 6 #include<iostream> 7 #include<vector> 8 #include<map> 9 #include<set> 10 #include<queue> 11 #include<string> 12 #include<bitset> 13 #define inf 1000000000 14 #define maxn 2000000+5 15 #define maxm 10000000 16 #define eps 1e-10 17 #define ll long long 18 #define pa pair<int,int> 19 #define for0(i,n) for(int i=0;i<=(n);i++) 20 #define for1(i,n) for(int i=1;i<=(n);i++) 21 #define for2(i,x,y) for(int i=(x);i<=(y);i++) 22 #define for3(i,x,y) for(int i=(x);i>=(y);i--) 23 #define for4(i,x) for(int i=head[x],y=e[i].go;i;i=e[i].next,y=e[i].go) 24 #define mod 1000000007 25 #define lch k<<1,l,mid 26 #define rch k<<1|1,mid+1,r 27 using namespace std; 28 inline int read() 29 { 30 int x=0,f=1;char ch=getchar(); 31 while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();} 32 while(ch>='0'&&ch<='9'){x=10*x+ch-'0';ch=getchar();} 33 return x*f; 34 } 35 int n,m,tot,head[maxn],id[maxn],pos[maxn],v[maxn]; 36 priority_queue<pa>q; 37 struct edge{int go,next;}e[maxn]; 38 inline void add(int x,int y) 39 { 40 e[++tot]=(edge){y,head[x]};head[x]=tot; 41 e[++tot]=(edge){x,head[y]};head[y]=tot; 42 } 43 int main() 44 { 45 freopen("input.txt","r",stdin); 46 freopen("output.txt","w",stdout); 47 n=read();m=read(); 48 for1(i,m)add(read(),read()); 49 for1(i,n)q.push(pa(0,i)); 50 for3(i,n,1) 51 { 52 while(id[q.top().second])q.pop(); 53 int x=q.top().second;q.pop(); 54 for4(j,x)if(!id[y])q.push(pa(++v[y],y)); 55 id[x]=i;pos[i]=x; 56 } 57 int ans=1; 58 for1(i,n) 59 { 60 int tmp=0; 61 for4(j,i)if(id[y]>id[i])tmp++; 62 ans=max(ans,tmp+1); 63 } 64 cout<<ans<<endl; 65 return 0; 66 }