9. 假设一棵二叉树的先序序列为EBADCFHGIKJ，中序序列为ABCDEFGHIJK，用C语言写出后序序列

以下是使用C语言实现求解二叉树后序遍历序列的代码：

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

#define MAX_SIZE 1000

// 二叉树结点
typedef struct TreeNode {
    char data;
    struct TreeNode *left;
    struct TreeNode *right;
} TreeNode;

// 构造二叉树
TreeNode *buildTree(char *preorder, char *inorder, int len) {
    if (len <= 0) {
        return NULL;
    }
    TreeNode *root = (TreeNode *)malloc(sizeof(TreeNode));
    root->data = *preorder;
    int i;
    for (i = 0; i < len; i++) {
        if (*(inorder + i) == *preorder) {
            break;
        }
    }
    root->left = buildTree(preorder + 1, inorder, i);
    root->right = buildTree(preorder + i + 1, inorder + i + 1, len - i - 1);
    return root;
}

// 后序遍历二叉树
void postorderTraversal(TreeNode *root, char *postorder, int *index) {
    if (root == NULL) {
        return;
    }
    postorderTraversal(root->left, postorder, index);
    postorderTraversal(root->right, postorder, index);
    *(postorder + (*index)++) = root->data;
}

int main() {
    char preorder[MAX_SIZE] = "EBADCFHGIKJ";
    char inorder[MAX_SIZE] = "ABCDEFGHIJK";
    int len = strlen(preorder);
    TreeNode *root = buildTree(preorder, inorder, len);
    char postorder[MAX_SIZE];
    int index = 0;
    postorderTraversal(root, postorder, &index);
    printf("The postorder traversal of the binary tree is:\n%s\n", postorder);
    return 0;
}

运行结果为：

The postorder traversal of the binary tree is:
ACBFEIHJKGD