集训day1 p1

二分图

貌似还有并查集  by wxr 改编自hnoi

#include <cstdio>
#include <cstring>
#include <iostream>
#define D 5010
using namespace std;
typedef pair<int,int> pii;
int pr[D],ptot,n,q,u,v,cnt,tim,col[D],abandoned[D];
int hash[D];
pii sav[D];
struct edge {
	int v,next;
}e[1000000];
int head[D];
int read () {
	char c = getchar();
	int re = 0;
	while(c > '9' || c < '0')
		c = getchar();
	while(c <= '9' && c >= '0') {
		re = re * 10 + c - '0';
		c = getchar();
	}
	return re;
}
void adde (int u,int v) {
	e[++cnt].v = v;
	e[cnt].next = head[u];
	head[u] = cnt;
	e[++cnt].v = u;
	e[cnt].next = head[v];
	head[v] = cnt;
}
void reverse (int U,int ti) {
	if(hash[U] == ti)
		return;
	col[U] ^= 1;
	hash[U] = ti;
	for(int i = head[U];i != -1;i = e[i].next) {
		int V = e[i].v;
		if(!abandoned[V])
			reverse(V,ti);
	}
}
int main () {
	freopen("traf.in","r",stdin);
	freopen("traf.out","w",stdout);
	memset(head,-1,sizeof head);
	n = read();
	q = read();
	for(int i = 1;i <= q;++i) {
		u = read();
		v = read();
		if(u > v) {
			int t = u;
			u = v;
			v = t;
		}
		sav[i].first = u;
		sav[i].second = v;
	}
	for(int i = 1;i <= q;i++) {
		for(int j = 1;j <= i - 1;++j) {
			if(!abandoned[j]) {
				if((((sav[j].first > sav[i].first) && (sav[j].first < sav[i].second)) && sav[j].second > sav[i].second)||(sav[j].first < sav[i].first && ((sav[j].second > sav[i].first) && sav[j].second < sav[i].second))) {
					if(col[i] != col[j] ^ 1) {
						reverse(i,++tim);
						if(col[i] != col[j] ^ 1) {
							abandoned[i] = 1;
							pr[++ptot] = i;
							break;
						}
						else adde(i,j);
					}
					else adde(i,j);
				}
			}
		}
	}
	printf("%d\n",ptot);
	for(int i = 1;i <= ptot;i++)
		printf("%d\n",pr[i]);
	return 0;
}