DFS_reverse

#include<iostream>
using namespace std;

const int MAXN = 100;
int U[MAXN+1],S[MAXN],P[MAXN],G[MAXN][MAXN],N;

void DFS_R(int r)
{   int y;
    while(G[r][0]>0)
    {  y=G[r][G[r][0]--];
       if(!U[y]) {U[y]=1; P[y]=r; DFS_R(y); }
    }
}

void first_call()
{ for(int i=1;i<=N;i++) U[i]=0;
  for(int i=1;i<=N;i++) if(U[i]==0)
      DFS_R(i);
}

int main(){

    int x,y;

    cin >> N;
    while( cin >> x >> y ){
    G[x][++G[x][0]] = y;
    G[y][++G[y][0]] = x;
    }

    DFS_R(1);

    for(int i=1; i<=10; i++ ) cout << i << " " << P[i] << endl;
    return 0;
}