c++写出默克树ABCDE的非递归前序遍历

非递归前序遍历默克树ABCDE的代码如下：

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

#define MAX_SIZE 100

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

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

TreeNode* createNode(char val) {
    TreeNode *node = (TreeNode*)malloc(sizeof(TreeNode));
    node->val = val;
    node->left = NULL;
    node->right = NULL;
    return node;
}

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

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

void preorderTraversal(TreeNode *root) {
    if (root == NULL) {
        return;
    }
    Stack stack;
    stack.top = -1;
    push(&stack, root);
    while (stack.top != -1) {
        TreeNode *node = pop(&stack);
        printf("%c ", node->val);
        if (node->right != NULL) {
            push(&stack, node->right);
        }
        if (node->left != NULL) {
            push(&stack, node->left);
        }
    }
}

int main() {
    TreeNode *A = createNode('A');
    TreeNode *B = createNode('B');
    TreeNode *C = createNode('C');
    TreeNode *D = createNode('D');
    TreeNode *E = createNode('E');

    A->left = B;
    A->right = C;
    B->left = D;
    C->left = E;

    printf("Preorder traversal of the Merkle tree: ");
    preorderTraversal(A);

    return 0;
}

输出结果为：`A B D C E`