leetcode 94.二叉树的中序遍历

给定一个二叉树的根节点 root ，返回它的 中序 遍历。

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */


/**
 * Note: The returned array must be malloced, assume caller calls free().
 */

int BinaryTreeSize(struct TreeNode* root)
{
    if(root==NULL)
    {
        return 0;
    }

    return BinaryTreeSize(root->left) + BinaryTreeSize(root->right) +1;
}


void _inorderTraversal(struct TreeNode* root, int* a,int* pi)
{
    if(root == NULL)
    {
        return;
    }

    //左子树
    _inorderTraversal(root->left, a,pi);

    //根
    a[(*pi)++] = root->val;

    //右子树
    _inorderTraversal(root->right, a,pi);
}



int* inorderTraversal(struct TreeNode* root, int* returnSize)
{
    //1.获取二叉树结点个数
    int size = BinaryTreeSize(root);

    //2.动态开辟数组
    int* a = (int*)malloc(sizeof(int)*size);

    //3.中序遍历，结点数据存入数组a中

    //数组初始下标
    int i = 0;

    _inorderTraversal(root, a, &i);

    *returnSize = size;
    return a;
}