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
 */

#include <string.h>
void preorderTraversalHelper(struct TreeNode* root, int* arr, int* returnSize) {
    if(root == NULL) return;
    arr[(*returnSize)++] = root->val;
    preorderTraversalHelper(root->left, arr, returnSize);
    preorderTraversalHelper(root->right, arr, returnSize);
}
int* preorderTraversal(struct TreeNode* root, int* returnSize ) {
    // write code here
    (*returnSize) = 0;
    int* arr = (int*)malloc(sizeof(int) * 100);
    preorderTraversalHelper(root , arr, returnSize);
    return arr;
}