CCF-CSP题解 201709-4 通信网络

dfs

#include <bits/stdc++.h>
const int maxn = 1000;
const int maxm = 10000;

using namespace std;

int to[maxm+10];
int nex[maxm+10];
int head[maxn+10], cnt = 0;

int know[maxn+10][maxn+10];

int vis[maxn+10];

void dfs(int r, int x)
{
    vis[x] = 1;
    know[r][x] = know[x][r] = 1;
    for (int i = head[x]; i != -1; i = nex[i])
    {
        int l = to[i];
        if (!vis[l])
        {
            dfs(r, l);
        }
    }
}

int main()
{
    int n, m;
    scanf("%d%d", &n, &m);

    memset(head, -1, sizeof(head));
    for (int i = 1, a, b; i <= m; i++)
    {
        scanf("%d%d", &a, &b);
        to[cnt] = b; nex[cnt] = head[a];
        head[a] = cnt++;
    }

    memset(know, 0, sizeof(know));

    for (int i = 1; i <= n; i++)
    {
        memset(vis, 0, sizeof(vis));
        dfs(i, i);
    }

    int ans = 0;
    for (int i = 1; i <= n; i++)
    {
        bool flag = true;
        for (int j = 1; j <= n; j++)
        {
            if (!know[i][j])
            {
                flag = false;
                break;
            }
        }
        if (flag)
        {
            ans++;
        }
    }

    printf("%d\n", ans);

    return 0;
}