第六课 DFS

伪代码(伪代码是用来记住算法的)

代码

#include <iostream>
#include <vector>
using namespace std;

#define Max 100
int n, m;    //n为点数，m为边数 
int clk;    //用于更新pre post
int pre[Max], post[Max]; 
bool vis[Max];
vector<int> v[Max];    //邻接表 

//开始访问x
void pre_vis(int x)
{
    pre[x] = clk;
    
    clk++;
}

//结束访问x 
void post_vis(int x)
{
    post[x] = clk;
    
    clk++;
}

//从x开始搜索 
void explore(int x)
{
    vis[x] = true;

    pre_vis(x);

    for (int i = 0; i < v[x].size(); ++i)
        if (!vis[v[x][i]])
            explore(v[x][i]);

    post_vis(x);
}

void dfs()
{
    //init
    clk = 1;
    
    for (int i = 1; i <= n; ++i)
        vis[i] = false;
    
    //explore 
    for (int i = 1; i <= n; ++i)
        if (!vis[i])
            explore(i); //explore次数为连通分量次数 
}

int main()
{
    cin >> n >> m;

    int a,b;
    for (int i = 0; i < m; ++i)
    {
        cin >> a >> b;

        v[a].push_back(b);
    }

    dfs();
}