hiho 53 連通性二·邊的雙連通分量

問題

http://hihocoder.com/problemset/problem/1184?sid=785059

解法

Tarjan算法+ 棧

#include <bits/stdc++.h>
using namespace std;
enum{maxn = 20000+4};
vector<int> G[maxn];
int n;
int parent[maxn];
int low[maxn];
int dfn[maxn];
int ss[maxn];
int group[maxn];
int visit[maxn];
int gNum;
void dfs(int u)
{
    static int count = 0;
    static int sCnt = -1;
    visit[u] = true;
    dfn[u] = low[u] = ++count;
    ss[++sCnt] = u;
    int start = sCnt;
    for (int i=0; i< G[u].size(); ++i)
    {
        int v = G[u][i];
        if (!visit[v])
        {
            parent[v] = u;
            dfs(v);
            low[u] = min(low[v], low[u]);
        }else{
            if (v != parent[u])
                low[u] = min(low[u], dfn[v]);
        }
    }
    if (low[u] == dfn[u])
    {
        ++gNum;
        int lt =INT_MAX;
        for (int i=start; i<= sCnt; ++i)
            lt = min(lt, ss[i]);
        for (int i=start; i<= sCnt; ++i)
            group[ss[i]] = lt;
        sCnt = start-1;
    }
}
int main()
{
    int m;
    scanf("%d %d", &n, &m);
    for (int i=0; i< m; ++i)
    {
        int a, b;
        scanf("%d %d", &a, &b);
        G[a].push_back(b);
        G[b].push_back(a);
    }
    parent[1] =  0;
    gNum = 0;
    dfs(1);
    printf("%d\n", gNum);
    for (int i=1; i<=n; ++i)
        printf("%d ", group[i]);
    putchar('\n');
    return 0;
}