这个代码是使用占位符的方式创建二叉树

#include "stdio.h"
#include "stdlib.h"

typedef struct node {
    char data;
    struct node *lchild;
    struct node *rchild;
} Node;

Node *create_node(char value) {
    Node *node = (Node *) malloc(sizeof(Node));
    if (node == NULL) {
        exit(-1);
    }

    node->data = value;
    node->lchild = NULL;
    node->rchild = NULL;
    return node;
}

//递归创建二叉树
Node *create_tree(char *preOrder, int *index) {
    char current = preOrder[*index];
    if (current == '#' || current == '\0') {
        *index = *index + 1;
        return NULL;
    }

    //创建当前节点
    Node *root = create_node(current);
    *index = *index + 1;
    root->lchild = create_tree(preOrder, index);
    root->rchild = create_tree(preOrder, index);
    return root;
}

void preOrderPrint(Node *node) {
    if (node == NULL) {
        return;
    }

    printf("%c ", node->data);
    preOrderPrint(node->lchild);
    preOrderPrint(node->rchild);
}

int main() {
    char preOrder[] = "AEB#C###D##";
    int index = 0;
    Node *root = create_tree(preOrder, &index);
    preOrderPrint(root);
    return 0;
}

运行效果