用c语言实现将二叉树的中序遍历，并将结点值保存在数组中

#include <stdio.h>

struct TreeNode {
    int val;
    struct TreeNode* left;
    struct TreeNode* right;
};

void inorderTraversalHelper(struct TreeNode* root, int* res, int* returnSize) {
    if (root != NULL) {
        inorderTraversalHelper(root->left, res, returnSize);
        res[(*returnSize)++] = root->val;
        inorderTraversalHelper(root->right, res, returnSize);
    }
}

int* inorderTraversal(struct TreeNode* root, int* returnSize) {
    *returnSize = 0;
    int* res = (int*)malloc(100 * sizeof(int));
    inorderTraversalHelper(root, res, returnSize);
    return res;
}

int main() {
    struct TreeNode a = { 1, NULL, NULL };
    struct TreeNode b = { 2, NULL, NULL };
    struct TreeNode c = { 3, NULL, NULL };
    struct TreeNode d = { 4, NULL, NULL };
    struct TreeNode e = { 5, NULL, NULL };

    a.left = &b;
    a.right = &c;
    b.right = &d;
    c.left = &e;

    int returnSize;
    int* res = inorderTraversal(&a, &returnSize);

    for (int i = 0; i < returnSize; i++) {
        printf("%d ", res[i]);
    }
    printf("\n");

    free(res);

    return 0;
}