C++

#include <iostream>
#include <stack>
#include <algorithm>
#include <string.h>
#include <vector>
using namespace std;
const int N = 1010, INF = 0x3f3f3f3f;

stack<int> level[N];    //use stack to find the father of current floder quickly
int pre[10010];         //locate path, since id are all 4-digit nums, we set size to 1e4
int n, k;

int main()
{

    memset(pre, 0x3f, sizeof(pre));     //pre[i] = INF means this node donesn't exist
    scanf("%d", &n);
    getchar();
    pre[0] = -1;                    //note the pre of root 0000 as -1, which tells the difference from thoses pre[]=INF
    for (int i = 0; i < n; i++ ) {
        string cid;
        getline(cin, cid);
        int l = count(cid.begin(), cid.end(), ' ');     //count spaces int cid, we can judge the level of its position
        int id = stoi(cid);     //stored in number format
        level[l].push(id);      //put to current level's stacks
        if (l > 0) {            //not the root floder
            int last = level[l - 1].top();  //search the last level's stack's top to find the father
            pre[id] = last;     //last->id, record path
        }
    }
    scanf("%d", &k);
    while (k-- ) {
        int id; scanf("%d", &id);
        if (pre[id] == INF) {   //this floder doesn't exist
            printf("Error: %04d is not found.", id);
        }
        else {
            vector<int> path;   //record path in reversed order
            while (id != -1) {
                path.push_back(id);
                id = pre[id];
            }
            for (int i = path.size() - 1; i >= 0; i-- ) {   //reprint in natural order
                printf("%04d", path[i]);
                if (i) printf("->");
            }
        }
        if (k) puts("");
    }
    // string s = "   12";
    // cout << stoi(s) << endl;
    return 0;
}