备战NOIP——模板复习23

这里只有模板，并不作讲解，仅为路过的各位做一个参考以及用做自己复习的资料，转载注明出处。

割点

/*Copyright: Copyright (c) 2018
*Created on 2018-11-07
*Author: 十甫
*Version 1.0 
*Title: 割点
*Time: inf mins
*/
#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;
const int maxn = 20005;
const int maxm = 100005;
inline int Min(int a, int b) {
	return a < b ? a : b;
}

int head[maxn];
struct edge {
	int to, next;
} data[maxm * 2];
inline void add_edge(int from, int to, int i) {
	data[i] = (edge) {to, head[from]};
	head[from] = i;
}
int n, m, dfn[maxn], low[maxn];
bool cut_vertex[maxn];

void dfs(int pos, int &ord, int from) {
	dfn[pos] = low[pos] = ord;
	int child = 0;
	for(int i = head[pos];i;i = data[i].next) {
		int u = data[i].to;
		if(!dfn[u]) {
			dfs(u, ++ord, pos);
			low[pos] = Min(low[pos], low[u]);
			if(low[u] >= dfn[pos] && pos != from) {
				cut_vertex[pos] = true;
			}
			if(pos == from) {
				child++;
			}
		}
		low[pos] = Min(low[pos], dfn[u]);
	}
	if(pos == from && child >= 2) {
		cut_vertex[pos] = true;
	}
}
void tarjan() {
	for(int i = 1;i <= n;i++) if(!dfn[i]) {
		int ord = 1;
		dfs(i, ord, i);
	}
}

int main() {
	scanf("%d%d", &n, &m);
	for(int i = 1;i <= m;i++) {
		int a, b;
		scanf("%d%d", &a, &b);
		add_edge(a, b, i), add_edge(b, a, i + m);
	}
	tarjan();
	int cnt = 0;
	for(int i = 1;i <= n;i++) if(cut_vertex[i]) {
		cnt++;
	}
	printf("%d
", cnt);
	for(int i = 1;i <= n;i++) if(cut_vertex[i]) {
		printf("%d ", i);
	}
	printf("
");
	return 0;
}