给定两个整数数组 preorder 和 inorder ，其中 preorder 是二叉树的先序遍历， inorder 是同一棵树的中序遍历，请构造二叉树并返回其根节点。
示例 1:
输入: preorder = [3,9,20,15,7], inorder = [9,3,15,20,7] 输出: [3,9,20,null,null,15,7]
示例 2:
输入: preorder = [-1], inorder = [-1] 输出: [-1]
代码：
/*** Definition for a binary tree node.* struct TreeNode {* int val;* struct TreeNode *left;* struct TreeNode *right;* };*/
struct TreeNode* buildTree(int* preorder, int preorderSize, int* inorder, int inorderSize) {if(preorderSize<=0||inorderSize<=0) return NULL;struct TreeNode *root=(struct TreeNode*)malloc(sizeof(struct TreeNode));int index;root->val=preorder[0];for(index=0;index<inorderSize;index++){if(inorder[index]==preorder[0]){break;}}root->left=buildTree(preorder+1,index,inorder,index);root->right=buildTree(preorder+1+index,preorderSize-1-index,inorder+1+index,inorderSize - index - 1);return root;
}