572. Subtree of Another Tree

https://leetcode.com/problems/subtree-of-another-tree

1. Use recursion:

//28 ms    18.5 MB
/**
 * 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 {
public:
    bool isSubtree(TreeNode* s, TreeNode* t) {
        if(!s) return false;
        bool isSub = false;
        bool isSubL = isSubtree(s->left, t);
        bool isSubR = isSubtree(s->right, t);
        if(s->val == t->val)
            isSub = isSameTree(s, t);
        return isSub || isSubL || isSubR;
    }
private:
    bool isSameTree(TreeNode* s, TreeNode* t) {
        if(!s && !t) return true;
        else if((!s && t) || (s && !t)) return false;
        bool isSubL = isSameTree(s->left, t->left);
        bool isSubR = isSameTree(s->right, t->right);
        if(s->val == t->val)
            return isSubL && isSubR;
        else
            return false;
    }
};