Coloring Edges（有向图环染色）-- Educational Codeforces Round 72 (Rated for Div. 2)

题意：https://codeforc.es/contest/1217/problem/D

给你一个有向图，要求一个循环里不能有相同颜色的边，问你最小要几种颜色染色，怎么染色？

思路：

如果没有环，那全是1；如果有环，那小到大的边为1，大到小的边为2。

 #define IOS ios_base::sync_with_stdio(0); cin.tie(0);
 #include <cstdio>//sprintf islower isupper
 #include <cstdlib>//malloc  exit strcat itoa system("cls")
 #include <iostream>//pair
 #include <fstream>//freopen("C:\\Users\\13606\\Desktop\\草稿.txt","r",stdin);
 #include <bitset>
 //#include <G>
 //#include<unordered_map>
 #include <vector>
 #include <stack>
 #include <set>
 #include <string.h>//strstr substr
 #include <string>
 #include <time.h>//srand(((unsigned)time(NULL))); Seed n=rand()%10 - 0~9;
 #include <cmath>
 #include <deque>
 #include <queue>//priority_queue<int, vector<int>, greater<int> > q;//less
 #include <vector>//emplace_back
 //#include <math.h>
 //#include <windows.h>//reverse(a,a+len);// ~ ! ~ ! floor
 #include <algorithm>//sort + unique : sz=unique(b+1,b+n+1)-(b+1);+nth_element(first, nth, last, compare)
 using namespace std;//next_permutation(a+1,a+1+n);//prev_permutation
 #define fo(a,b,c) for(register int a=b;a<=c;++a)
 #define fr(a,b,c) for(register int a=b;a>=c;--a)
 #define mem(a,b) memset(a,b,sizeof(a))
 #define pr printf
 #define sc scanf
 #define ls rt<<1
 #define rs rt<<1|1
 typedef long long ll;
 void swapp(int &a,int &b);
 double fabss(double a);
 int maxx(int a,int b);
 int minn(int a,int b);
 int Del_bit_1(int n);
 int lowbit(int n);
 int abss(int a);
 //const long long INF=(1LL<<60);
 const double E=2.718281828;
 const double PI=acos(-1.0);
 const int inf=(<<);
 const double ESP=1e-;
 const int mod=(int)1e9+;
 const int N=(int)1e6+;

 int in[N];
 vector<vector<int> > G(N);

 bool top_sort(int n)
 {
     int cont=;
     queue<int> q;
     for(int i=;i<=n;i++)
         if(in[i]==)
             q.push(i);
     while(!q.empty())
     {
         int x=q.front();
         q.pop();
         cont++;
         for(int i=;i<G[x].size();i++)
         {
             in[G[x][i]]--;
             if(in[G[x][i]]==)
                 q.push(G[x][i]);
         }
     }
     return (cont==n);
 }
 struct node
 {
     int u,v;
 }edge[N];

 int main()
 {
     int n,m;
     sc("%d%d",&n,&m);
     for(int i=;i<=m;++i)
     {
         int u,v;
         sc("%d%d",&u,&v);
         edge[i]={u,v};
         in[v]++;
         G[u].push_back(v);
     }
     if(top_sort(n))
     {
         pr("1\n");
         for(int i=;i<=m;++i)
             pr("1 ");
     }
     else
     {
         pr("2\n");
         for(int i=;i<=m;++i)
             pr("%d ",edge[i].u>edge[i].v?:);
     }
     return ;
 }

 /**************************************************************************************/

 int maxx(int a,int b)
 {
     return a>b?a:b;
 }

 void swapp(int &a,int &b)
 {
     a^=b^=a^=b;
 }

 int lowbit(int n)
 {
     return n&(-n);
 }

 int Del_bit_1(int n)
 {
     return n&(n-);
 }

 int abss(int a)
 {
     return a>?a:-a;
 }

 double fabss(double a)
 {
     return a>?a:-a;
 }

 int minn(int a,int b)
 {
     return a<b?a:b;
 }