P1347 sorting (TOPO)

P1347 Sort (topo)

Deepened topo The understanding of the .

situation 1： It's stable topo, The number of layers is n Chain .

situation 2： Ring , The way to judge the ring is that there are nodes that are not in the queue .

situation 3： Non case 1 and 2, Namely 3.

It is worth noting that the situation 1 Is aimed at n Nodes , situation 2 It is aimed at the current pre - x Ring of nodes .

// Problem: P1347  Sort 
// Contest: Luogu
// URL: https://www.luogu.com.cn/problem/P1347
// Memory Limit: 125 MB
// Time Limit: 1000 ms
// Date: 2022-06-22 10:02:38
// --------by Herio--------

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull; 
const int N=1e3+5,M=2e4+5,inf=0x3f3f3f3f,mod=1e9+7;
const int hashmod[4] = {
    402653189,805306457,1610612741,998244353};
#define mst(a,b) memset(a,b,sizeof a)
#define db double
#define PII pair<int,int>
#define PLL pair<ll,ll>
#define x first
#define y second
#define pb emplace_back
#define SZ(a) (int)a.size()
#define rep(i,a,b) for(int i=a;i<=b;++i)
#define per(i,a,b) for(int i=a;i>=b;--i)
#define IOS ios::sync_with_stdio(false),cin.tie(nullptr) 
void Print(int *a,int n){
    
	for(int i=1;i<n;i++)
		printf("%d ",a[i]);
	printf("%d\n",a[n]); 
}
template <typename T>		//x=max(x,y) x=min(x,y)
void cmx(T &x,T y){
    
	if(x<y) x=y;
}
template <typename T>
void cmn(T &x,T y){
    
	if(x>y) x=y;
}
vector<int>e[N];
int _in[N],in[N];
bitset<N>vis;
int d[26];
int n,m;
void topo(int r){
    
	queue<int>q;
	memcpy(in,_in,sizeof in);
	int cnt = 0;
	vector<int>ans;
	mst(d,0);
	int _n = 0;
	for(int i=0;i<26;i++) if(vis[i]) _n++;
	for(int i=0;i<26;i++)
		if(vis[i] &&  !in[i]){
    
			q.push(i);
			cnt++;
		}
	int mx = 0;
	while(!q.empty()){
    
		int u = q.front();q.pop();
		ans.pb(u);
		cmx(mx,d[u]);
		for(int v:e[u]){
    
			if(!--in[v]){
    
				q.push(v);
				d[v] = d[u] + 1;
				cnt++;
			}
		}
	}
	if(mx==n-1){
    
		printf("Sorted sequence determined after %d relations: ",r);
		for(int x:ans) printf("%c",x+'A');
		puts(".");
		exit(0);
	}
	else if(cnt<_n){
    
		printf("Inconsistency found after %d relations.",r);
		exit(0);
	}
}
int main(){
    
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++){
    
		string s;
		cin>>s;
		e[s[0]-'A'].pb(s[2]-'A');
		vis[s[0]-'A'] = vis[s[2]-'A'] = true;
		_in[s[2]-'A']++;
		topo(i);
	}
	puts("Sorted sequence cannot be determined.");
	return 0;
}