subtree-of-another-tree

Subtree of Another Tree – LeetCode 572

Problem

Description

Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node’s descendants. The tree s could also be considered as a subtree of itself.

Answer

Original

Code

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

思路

优先寻找潜在子树头，找到后使用check检查。时间复杂度$O(m \times n)$，空间复杂度$O(m)$。
耗时$16$ ms，排名$5.75\%$

Better

思路

还没看到更好的思路。