LintCode 375. 克隆二叉树(深复制)

先序遍历+构造二叉树

TreeNode * preorder(TreeNode * root){
    if(root==NULL) return NULL;
    TreeNode * ans;
    ans=new TreeNode(root->val);
    if(root->left!=NULL){
        ans->left=preorder(root->left);
    }
    if(root->right!=NULL){
        ans->right=preorder(root->right);
    }
    return ans;
}