codeforces # 1217D. Coloring Edges (staining on map)

Topic links:

https://codeforces.com/contest/1217/problem/D

Meaning of the questions:

FIG contracted to $ k $ colors, the same color can not form a ring

data range:

$ 1 \ leq n \ leq $ 5,000

$ 1 \ leq m \ leq 5000 $

analysis: 

Category talk:

1, there is no ring, coated with a clear color

2, there is a ring, then sure, each ring has at least one side of a large number of the node from a large number of the node to a small number of the node, a small number of the node to the edge

Then, a first edge to a color infected, infected with the second side of another color, the same color definitely not present to form a ring

 

AC Code:

#include<bits/stdc++.h>
#define ll long long
#define pii pair<int,int>
using namespace std;
const int maxn=5000+7;
struct Edge{
    int a,b,color;
}edge[maxn];
int n,m,vis[maxn],now,k=1;
vector<int>ve[maxn];
void dfs(int x){
    if(vis[x]){
        if(x==now)k=2;
        return ;
    }
    vis[x]=1;
    for(int i=0;i<ve[x].size();i++)
        dfs(ve[x][i]);
}

int main()
{
    scanf("%d %d",&n,&m);
    for(int i=1;i<=m;i++){
        int a,b;
        scanf("%d %d",&a,&b);
        edge[i]=(Edge){a,b,-1};
        ve[a].push_back(b);
    }
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++)vis[j]=0;
        now=i;
        dfs(i);
    }

    for(int i=1;i<=m;i++){
        if(k==1||edge[i].a>edge[i].b)edge[i].color=1;
        else edge[i].color=2;
    }
    printf("%d\n",k);
    for(int i=1;i<=m;i++){
        printf("%d",edge[i].color);
        if(i!=m)printf(" ");
        else printf("\n");
    }
    return 0;
}