题解

#include <bits/stdc++.h>
using namespace std;

struct Node {
    int left, right;
};
Node tree[101];
void preorder(int root) {
    if (root == 0) return;
    cout << root << " ";
    preorder(tree[root].left);
    preorder(tree[root].right);
}
void inorder(int root) {
    if (root == 0) return;
    inorder(tree[root].left);
    cout << root << " ";
    inorder(tree[root].right);
}
void postorder(int root) {
    if (root == 0) return;
    postorder(tree[root].left);
    postorder(tree[root].right);
    cout << root << " ";
}

int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        int idx, left, right;
        cin >> idx >> left >> right;
        tree[idx].left = left;


        tree[idx].right = right;
    }
    int root = 1;
    preorder(root);
    cout << endl;
    inorder(root);
    cout << endl;
    postorder(root);
    cout << endl;
    return 0;
}