题解 | #二叉树的前序遍历#

/**
 * struct TreeNode {
 *  int val;
 *  struct TreeNode *left;
 *  struct TreeNode *right;
 * };
 */
/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 *
 * @param root TreeNode类
 * @return int整型一维数组
 * @return int* returnSize 返回数组行数
 */
static int num = 0;
void preOrder(struct TreeNode* root, int* res) {
    if (root == NULL)
        return;
    res[num] = root->val;
    num++;
    preOrder(root->left, res);
    preOrder(root->right, res);
}

int* preorderTraversal(struct TreeNode* root, int* returnSize) {
    if (root == NULL)
        return NULL;
    int* ret = (int*)malloc(sizeof(int) * 100);
    preOrder(root, ret);
    *returnSize = num;
    return ret;
}