#include <stdio.h>
#include <stdlib.h>
typedef struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
} TreeNode; 
TreeNode* createNode(int value) {// 创建新节点
    TreeNode *newNode = (TreeNode*)malloc(sizeof(TreeNode));
    newNode->val = value;
    newNode->left = NULL;
    newNode->right = NULL;
    return newNode;
}
void preorderTraversal(TreeNode *root) {
    if (root == NULL) return;
    printf("%d ", root->val);  // 访问根节点
    preorderTraversal(root->left);  // 遍历左子树
    preorderTraversal(root->right); // 遍历右子树
}
void inorderTraversal(TreeNode *root) {
    if (root == NULL) return;
    inorderTraversal(root->left);  // 遍历左子树
    printf("%d ", root->val);      // 访问根节点
    inorderTraversal(root->right); // 遍历右子树
}
void postorderTraversal(TreeNode *root) {
    if (root == NULL) return;
    postorderTraversal(root->left);  // 遍历左子树
    postorderTraversal(root->right); // 遍历右子树
    printf("%d ", root->val);        // 访问根节点
}
int main() {
    // 创建二叉树
    TreeNode *root = createNode(1);
    root->left = createNode(2);
    root->right = createNode(3);
    root->left->left = createNode(4);
    root->left->right = createNode(5);

    printf("前序遍历: ");
    preorderTraversal(root);
    printf("\n");
    printf("中序遍历: ");
    inorderTraversal(root);
    printf("\n");
    printf("后序遍历: ");
    postorderTraversal(root);
    printf("\n");
    return 0;
}