ACM模版

无向图找桥

/* * 无向图找桥 * INIT: edge[][]邻接矩阵；vis[],pre[],ans[],bridge置0； * CALL: dfs(0, -1, 1, n); */

const int V = 1010;

int bridge; //桥
int edge[V][V];
int ans[V];
int pre[V];
int vis[V];

void dfs(int cur, int father, int dep, int n)
{
    //vertex: 0 ~ n - 1
    if (bridge)
    {
        return ;
    }
    vis[cur] = 1;
    pre[cur] = ans[cur] = dep;

    for (int i = 0; i < n; i++)
    {
        if (edge[cur][i])
        {
            if (i != father && 1 == vis[i])
            {
                if (pre[i] < ans[cur])
                {
                    ans[cur] = pre[i];  //back edge
                }
            }
            if (0 == vis[i])    //tree edge
            {
                dfs(i, cur, dep + 1, n);
                if (bridge)
                {
                    return ;
                }
                if (ans[i] < ans[cur])
                {
                    ans[cur] = ans[i];
                }
                if (ans[i] > pre[cur])
                {
                    bridge = 1;
                    return ;
                }
            }
        }
    }
    vis[cur] = 2;
    return ;
}