c语言非递归中序遍历二叉树

下面是 C 语言非递归中序遍历二叉树的代码：

#include <stdio.h>
#include <stdlib.h>

#define MAX_STACK_SIZE 100

typedef struct TreeNode {
    int val;
    struct TreeNode* left;
    struct TreeNode* right;
} TreeNode;

typedef struct Stack {
    TreeNode* data[MAX_STACK_SIZE];
    int top;
} Stack;

void push(Stack* s, TreeNode* node) {
    if (s->top == MAX_STACK_SIZE - 1) {
        printf("Stack overflow!\n");
        return;
    }
    s->data[++s->top] = node;
}

TreeNode* pop(Stack* s) {
    if (s->top == -1) {
        printf("Stack underflow!\n");
        return NULL;
    }
    return s->data[s->top--];
}

int is_empty(Stack* s) {
    return s->top == -1;
}

void inorder_traversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    Stack s;
    s.top = -1;
    TreeNode* p = root;
    while (p != NULL || !is_empty(&s)) {
        while (p != NULL) {
            push(&s, p);
            p = p->left;
        }
        if (!is_empty(&s)) {
            p = pop(&s);
            printf("%d ", p->val);
            p = p->right;
        }
    }
}

int main() {
    /*
     * 构造一棵二叉树如下:
     *      1
     *     / \
     *    2   3
     *   / \   \
     *  4   5   6
     */
    TreeNode* root = (TreeNode*)malloc(sizeof(TreeNode));
    root->val = 1;
    root->left = (TreeNode*)malloc(sizeof(TreeNode));
    root->left->val = 2;
    root->left->left = (TreeNode*)malloc(sizeof(TreeNode));
    root->left->left->val = 4;
    root->left->left->left = NULL;
    root->left->left->right = NULL;
    root->left->right = (TreeNode*)malloc(sizeof(TreeNode));
    root->left->right->val = 5;
    root->left->right->left = NULL;
    root->left->right->right = NULL;
    root->right = (TreeNode*)malloc(sizeof(TreeNode));
    root->right->val = 3;
    root->right->left = NULL;
    root->right->right = (TreeNode*)malloc(sizeof(TreeNode));
    root->right->right->val = 6;
    root->right->right->left = NULL;
    root->right->right->right = NULL;

    printf("Inorder traversal: ");
    inorder_traversal(root);
    printf("\n");

    return 0;
}

输出结果为：

Inorder traversal: 4 2 5 1 3 6