函数名为 char* getpost(char preA[],char inA[],int N)

好的，那么以下是函数名为 `char* getpost(char preA[], char inA[], int N)` 的代码实现：

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

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

int find_idx(char *inorder, int start, int end, char target) {
    for (int i = start; i <= end; i++) {
        if (inorder[i] == target) {
            return i;
        }
    }
    return -1;
}

TreeNode* buildTree(char* preorder, int preStart, int preEnd, char* inorder, int inStart, int inEnd) {
    if (preStart > preEnd || inStart > inEnd) {
        return NULL;
    }

    TreeNode *root = (TreeNode*)malloc(sizeof(TreeNode));
    root->val = preorder[preStart];
    root->left = NULL;
    root->right = NULL;

    int rootIdx = find_idx(inorder, inStart, inEnd, preorder[preStart]);
    int leftLen = rootIdx - inStart;
    int rightLen = inEnd - rootIdx;

    root->left = buildTree(preorder, preStart + 1, preStart + leftLen, inorder, inStart, rootIdx - 1);
    root->right = buildTree(preorder, preEnd - rightLen + 1, preEnd, inorder, rootIdx + 1, inEnd);

    return root;
}

void postorder(TreeNode *root, char *result, int *idx) {
    if (root == NULL) {
        return;
    }

    postorder(root->left, result, idx);
    postorder(root->right, result, idx);

    result[*idx] = root->val;
    (*idx)++;
}

char* getpost(char preA[], char inA[], int N) {
    TreeNode *root = buildTree(preA, 0, N - 1, inA, 0, N - 1);
    char *result = (char*)malloc(sizeof(char) * (N + 1));
    memset(result, 0, sizeof(char) * (N + 1));
    int idx = 0;
    postorder(root, result, &idx);
    return result;
}

int main() {
    char preA[] = "ABDEGCHF";
    char inA[] = "DBEGAHCF";
    int N = sizeof(preA) / sizeof(preA[0]);

    char *postA = getpost(preA, inA, N);

    printf("%s", postA);

    free(postA);

    return 0;
}

其中，`getpost`函数根据先序遍历序列和中序遍历序列构造出二叉树，并返回二叉树的后序遍历序列。`postorder`函数实现后序遍历二叉树，并将结果存储在`result`数组中，`idx`变量表示存储结果的数组下标。