图的遍历

#include <cstdio>
#include <iostream>
#define maxlen 100005
using namespace std;
int n, m;
int u[maxlen], v[maxlen];
int first[maxlen], next1[maxlen];
void dfs()
{

    for (int i = 1; i <=n; i++)
    {
        int k = first[i];
        while (k != -1)
        {
            cout << u[k] << v[k];
            k = next1[k];
        }
    }

}

int main()
{
    int mm;
    cin>>n>>m;
    mm=m;
    for (int i = 1; i <= n; i++)
        first[i] = -1;
    for (int i = 1; i <= m; i++)
    {
        cin >> u[i] >> v[i];
        next1[i] = first[u[i]];
        first[u[i]] = i;
    }
    dfs();
    return 0;
}
/*
5 4
1 2
2 4
4 3
4 5
*/