572. Subtree of Another Tree ------E

Given the roots of two binary trees root and subRoot, return true if there is a subtree of root with the same structure and node values of subRoot and false otherwise.

A subtree of a binary tree tree is a tree that consists of a node in tree and all of this node's descendants. The tree tree could also be considered as a subtree of itself.

 

Example 1:

Input: root = [3,4,5,1,2], subRoot = [4,1,2]
Output: true

Example 2:

Input: root = [3,4,5,1,2,null,null,null,null,0], subRoot = [4,1,2]
Output: false

 

Constraints:

• The number of nodes in the root tree is in the range [1, 2000].
• The number of nodes in the subRoot tree is in the range [1, 1000].
• -104 <= root.val <= 104
• -104 <= subRoot.val <= 104

A:

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    bool isSubtree(TreeNode* root, TreeNode* subRoot) {
        if(!root){
            return subRoot == nullptr;
        }
        return isMatch(root, subRoot) || 
            isSubtree(root->left, subRoot) ||
            isSubtree(root->right, subRoot);
        }
private: 
    bool isMatch(TreeNode* root, TreeNode* subRoot){
        if(!root && !subRoot){
            return true;
        }else if(!root || ! subRoot){
            return false;
        }else{
            return (root->val == subRoot->val) &&
             isMatch(root->left, subRoot->left) && 
             isMatch(root->right, subRoot->right);
        }
    }
};