1013 Battle Over Cities

• dfs确定连通块数量

const int N = 1e6 + 10, M = 2 * N, INF = 0x3f3f3f3f;
int n, m, k, h[N], e[M], ne[M], idx = 0;
bool visited[N];
void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}

void dfs(int u, int x)
{
    visited[u] = true;
    for(int v = h[u]; v != -1; v = ne[v])
    {
        int j = e[v];
        if(visited[j] == false)
        {
            dfs(j, x);
        }
    }
}

int find_repaired_highways(int x)
{
    fill(visited, visited + N, false);
    int cnt = 0;
    visited[x] = true;
    for(int i = 1; i <= n; ++i)
    {
        if(visited[i] == false)
        {
            dfs(i, x);
            cnt++;
        }
    }
    return cnt - 1;
}

int main()
{
    fill(h, h + N, -1);
    cin >> n >> m >> k;
    while(m--)
    {
        int a, b;
        cin >> a >> b;
        add(a, b);
        add(b, a);
    }
    while(k--)
    {
        int x;
        cin >> x;
        
        int ret = find_repaired_highways(x);
        cout << ret << endl;
    }
    return 0;
}