[ZOJ1015]：Fishing Net

题面

Vjudge

Sol

给出一个n个点的无向图，询问是否为弦图

做法见上上上篇博客

# include <bits/stdc++.h>
# define RG register
# define IL inline
# define Fill(a, b) memset(a, b, sizeof(a))
using namespace std;
const int _(1005);
typedef long long ll;

IL int Input(){
    RG int x = 0, z = 1; RG char c = getchar();
    for(; c < '0' || c > '9'; c = getchar()) z = c == '-' ? -1 : 1;
    for(; c >= '0' && c <= '9'; c = getchar()) x = (x << 1) + (x << 3) + (c ^ 48);
    return x * z;
}

int n, m, first[_], cnt, label[_], vis[_], best, Q[_], id[_], S[_];
struct Edge{
    int to, next;
} edge[_ * _];
vector <int> P[_];

IL void Add(RG int u, RG int v){
    edge[cnt] = (Edge){v, first[u]}, first[u] = cnt++;
}

IL int Check(){
	for(RG int i = 1; i <= n; ++i) vis[i] = 0;
	for(RG int i = n; i; --i){
		RG int ret = 1; S[0] = 0;
		for(RG int e = first[Q[i]]; e != -1; e = edge[e].next)
			if(id[edge[e].to] > i) vis[S[++S[0]] = edge[e].to] = 1;
		for(RG int e = first[S[1]]; e != -1; e = edge[e].next)
			if(edge[e].to != S[1] && vis[edge[e].to])
				ret += (vis[edge[e].to] == 1), ++vis[edge[e].to];
		for(RG int j = 1; j <= S[0]; ++j) vis[S[j]] = 0;
		if(S[0] && ret != S[0]) return 0;
	}
	return 1;
}

int main(RG int argc, RG char* argv[]){
	while(233){
		n = Input(), m = Input();
		if(!n && !m) break;
		cnt = best = 0;
		for(RG int i = 1; i <= n; ++i) P[i].clear(), first[i] = -1, vis[i] = label[i] = 0;
		for(RG int i = 1; i <= m; ++i){
			RG int u = Input(), v = Input();
			Add(u, v), Add(v, u);
		}
		for(RG int i = 1; i <= n; ++i) P[0].push_back(i);
		for(RG int i = n, nw; i; --i){
			for(RG int flg = 0; !flg; ){
				for(RG int j = P[best].size() - 1; ~j; --j)
					if(vis[P[best][j]]) P[best].pop_back();
					else{
						nw = P[best][j], flg = 1;
						break;
					}
				if(!flg) --best;
			}
			vis[nw] = 1, Q[i] = nw, id[nw] = i;
			for(RG int e = first[nw]; e != -1; e = edge[e].next)
				if(!vis[edge[e].to]){
					P[++label[edge[e].to]].push_back(edge[e].to);
					best = max(best, label[edge[e].to]);
				}
		}
		Check() ? puts("Perfect") : puts("Imperfect");
		puts("");
	}
    return 0;
}