打印二叉树后序遍历时栈的情况

#include <stdio.h>
#include <stdlib.h>
#define MAX_SIZE (1 << 8)

typedef char ElementType;

struct TreeNode {
  struct TreeNode *left, *right;
  ElementType data;
};

typedef struct TreeNode TreeNode;
typedef TreeNode *BiTree;

// 定义一个树
char str[] = "ABDH#K###E##CFI###G#J##";
int Index = 0;

// 定义栈，存储节点的值、左子树的值和右子树的值
struct Stack {
  ElementType val, left, right;
} stack[MAX_SIZE];
// char stack[MAX_SIZE];
int top = -1;

// 树的创建
BiTree create_tree() {
  ElementType ch = str[Index++];

  // 遇到空节点
  if (ch == '#') {
    return NULL;
  } else {
    TreeNode *T = (BiTree)malloc(sizeof(TreeNode));

    T->data = ch;
    T->left = create_tree();
    T->right = create_tree();
    return T;
  }
}

// 打印栈
void print_stack() {
  printf("---------------\n");
  for (int i = top; i >= 0; i--) {
    printf("| post(%c) %c, %c|", stack[i].val, stack[i].left, stack[i].right);
    if (i == top)
      printf(" <-stack top");
    printf("\n");
  }
  printf("---------------\n");
}

// 前序
void pre_order(BiTree T) {
  if (T == NULL)
    return;

  printf("%c", T->data);
  pre_order(T->left);
  pre_order(T->right);
}

// 中序
void in_order(BiTree T) {
  if (T == NULL)
    return;

  in_order(T->left);
  printf("%c", T->data);
  in_order(T->right);
}

// 后序
void post_order(BiTree T) {
  if (T == NULL)
    return;

  post_order(T->left);
  post_order(T->right);
  printf("%c\n", T->data);
}

// 后序，在输出打印后序节点的时候，打印栈的情况
void post_order_print_stack(BiTree T) {
  if (T == NULL)
    return;

  printf("+ %c: call post(%c)\n", T->data, T->data);

  char left, right;
  left = (T->left == NULL) ? '#' : T->left->data;
  right = (T->right == NULL) ? '#' : T->right->data;
  stack[++top] = (struct Stack){T->data, left, right}; // 入栈

  post_order_print_stack(T->left);
  post_order_print_stack(T->right);
  print_stack();                        // 打印栈的情况
  printf("output node: %c\n", T->data); // 输出后序遍历的节点

  printf("- %c: ret  post(%c)\n", T->data, T->data);
  --top;
}

int main() {
  BiTree T = create_tree();

  /*
  printf("pre order:");
  pre_order(T);
  puts("");

  printf("in order:");
  in_order(T);
  puts("");
  */

  printf("post order:\n");
  post_order_print_stack(T);

  return 0;
}