逆天

#include<iostream>
using namespace std;
struct TreeNode {
    int left, right;
    TreeNode(int left, int right) {left = left, right = right;}
    TreeNode() {}
} tree[100005];
int n;
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() {
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    cin >> n;
    for (int i = 1; i <= n; i++) {
        int l, r; cin >> l >> r;
        tree[i] = TreeNode(l, r);
    }
    preorder(1); cout << endl;
    inorder(1); cout << endl;
    postorder(1); cout << endl;
    return 0;
}