Tarjan 无向图计算最大环(最小环) java实现 Poj3895

Tarjan计算最大环(或者最小环)

题目链接:Cycles of Lanes

最大环模板题

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayDeque;
import java.util.LinkedList;
import java.util.StringTokenizer;

public class Main {
static int[] dfn,low;
static boolean[] visit;
static LinkedList[] adj;
static int visitCnt,result;
static ArrayDeque stack;

public static void main(String[] args) throws Exception{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer st = new StringTokenizer(br.readLine());
int T = Integer.parseInt(st.nextToken());
for(int testcase = 1;testcase<=T;testcase++){
st = new StringTokenizer(br.readLine());
int n = Integer.parseInt(st.nextToken());
int m = Integer.parseInt(st.nextToken());
dfn = new int[n+1];
low = new int[n+1];
visit = new boolean[n+1];
adj = new LinkedList[n+1];
stack = new ArrayDeque();
for(int i = 0;i<adj.length;i++){
adj[i] = new LinkedList();
}
result = 0;

int from,to;
for(int i = 0;i<m;i++){
st = new StringTokenizer(br.readLine());
from = Integer.parseInt(st.nextToken());
to = Integer.parseInt(st.nextToken());
adj[from].add(to);
adj[to].add(from);
}

for(int i = 1;i<=n;i++){
if(!visit[i]){
tarjan(i,-1);
}
}
System.out.println(result);
}
}

private static void tarjan(int from,int fromParent){
dfn[from] = low[from] = ++visitCnt;
visit[from] = true;
stack.push(from);
for(int to:adj[from]){
if(to == fromParent){
continue;
}
if(dfn[to] == 0){
int temp = visitCnt;
tarjan(to,from);
visitCnt = temp;
low[from] = Math.min(low[from],low[to]);
}
else if(visit[to]){
low[from] = Math.min(low[from],dfn[to]);
result = Math.max(result,dfn[from]-dfn[to]+1);
}
}

if(dfn[from] == low[from]){
int popPoint;
do{
popPoint = stack.pop();
visit[popPoint] = false;
}while (dfn[popPoint]!=low[popPoint]);
}
}
}