[TJOI2007]小朋友

题面

Luogu

Sol

弦图最大独立集

做法见上篇博客

# include <bits/stdc++.h>
# define RG register
# define IL inline
# define Fill(a, b) memset(a, b, sizeof(a))
using namespace std;
const int _(205);
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[_], ans, best, Q[_];
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++;
}

int main(RG int argc, RG char* argv[]){
	Fill(first, -1), Q[0] = n = Input(), m = Input();
	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 = 1, nw; i <= n; ++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[Q[0]--] = nw;
		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]);
			}
	}
	Fill(vis, 0);
	for(RG int i = 1; i <= n; ++i){
		if(vis[Q[i]]) continue;
		++ans, vis[Q[i]] = 1;
		for(RG int e = first[Q[i]]; e != -1; e = edge[e].next)
			vis[edge[e].to] = 1;
	}
	printf("%d\n", ans);
    return 0;
}