LeetCode 623. Add One Row to Tree

给定一个数字v和k，在树的第k层插入一层v

采用递归的办法，根节点因为没有根节点，要特殊处理一下

 

class Solution {
public:
    TreeNode* helper(TreeNode* node, int v, int d, bool bLeft) {
        if(d==1){
            TreeNode* head=new TreeNode(v);
            if(bLeft)
                head->left=node;
            else
                head->right=node;
            return head;
        }
        
        if(!node)
            return NULL;
        
        node->left = helper(node->left, v, d-1, true);
        node->right = helper(node->right, v, d-1, false);
        return node;
    }
    
    TreeNode* addOneRow(TreeNode* root, int v, int d) {
        if(d==1){
            TreeNode* head=new TreeNode(v);
            head->left=root;
            return head; 
        }
        
        if(!root)
            return NULL;
        
        root->left=helper(root->left, v, d-1, true);
        root->right=helper(root->right, v, d-1, false);
        return root;
    }
};