【力扣】94. 二叉树的中序遍历、144. 二叉树的前序遍历、145. 二叉树的后序遍历

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
void inorder(struct TreeNode* root, int* res, int* resSize) {
    if (!root) {
        return;
    }
    inorder(root->left, res, resSize);  // 左子树
    res[(*resSize)++] = root->val;      // 根节点
    inorder(root->right, res, resSize); // 右子树
}
/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* inorderTraversal(struct TreeNode* root, int* returnSize) {
    int* res = malloc(sizeof(int) * 501);
    *returnSize = 0;
    inorder(root, res, returnSize);
    return res;
}

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
void preorder(struct TreeNode* root, int* res, int* resSize) {
    if (!root) {
        return;
    }
    res[(*resSize)++] = root->val;       // 根节点
    preorder(root->left, res, resSize);  // 左子树
    preorder(root->right, res, resSize); // 右子树
}
/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* preorderTraversal(struct TreeNode* root, int* returnSize) {
    int* res = malloc(sizeof(int) * 501);
    *returnSize = 0;
    preorder(root, res, returnSize);
    return res;
}

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
void postorder(struct TreeNode* root, int* res, int* resSize) {
    if (!root) {
        return;
    }
    postorder(root->left, res, resSize);  // 左子树
    postorder(root->right, res, resSize); // 右子树
    res[(*resSize)++] = root->val;        // 根节点
}
/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* postorderTraversal(struct TreeNode* root, int* returnSize) {
    int* res = malloc(sizeof(int) * 501);
    *returnSize = 0;
    postorder(root, res, returnSize);
    return res;
}