全ACGO唯一链表做法

#include <iostream>
using namespace std;

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};

void preOrder(TreeNode *root) {
    if(root == nullptr) return;
    cout << root->val << " ";
    preOrder(root->left);
    preOrder(root->right);
}
void inOrder(TreeNode *root) {
    if(root == nullptr) return;
    inOrder(root->left);
    cout << root->val << " ";
    inOrder(root->right);
}
void postOrder(TreeNode *root) {
    if(root == nullptr) return;
    postOrder(root->left);
    postOrder(root->right);
    cout << root->val << " ";
}

int main() {
    int n;
    cin >> n;
    TreeNode* tree[105] = {nullptr};
    for(int i = 1; i <= n; i++) {
        tree[i] = new TreeNode(i);
    }
    for(int i = 1; i <= n; i++) {
        int u,l,r;
        cin >> u >> l >> r;
        if(l != 0) tree[u]->left = tree[l];
        if(r != 0) tree[u]->right = tree[r];
    }
    TreeNode *root = tree[1];
    
    preOrder(root);
    cout << endl;
    inOrder(root);
    cout << endl;
    postOrder(root);
    cout << endl;
    return 0;
}