struct TreeNode * build(int * in,int *pre,const int isz,int left,int right,int *ptr)
{
    if(left >= right || *ptr >= isz)
        return NULL;
    int mid = left;
    while(pre[*ptr] != in[mid]) mid++;
    struct TreeNode * root = malloc(sizeof(struct TreeNode));
    root->val = pre[(*ptr)++];
    root->left = build(in,pre,isz,left,mid,ptr);
    root->right = build(in,pre,isz,mid+1,right,ptr);
    return root;
}
struct TreeNode* buildTree(int* preorder, int preorderSize, int* inorder, int inorderSize) {
    int ptr = 0;
    return build(inorder,preorder,inorderSize,0,inorderSize,&ptr);
}