572. Subtree of Another Tree

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.

Example 1:
Given tree s:

     3
    / 
   4   5
  / 
 1   2

Given tree t:

   4 
  / 
 1   2

Return true, because t has the same structure and node values with a subtree of s.

 

Example 2:
Given tree s:

     3
    / 
   4   5
  / 
 1   2
    /
   0

Given tree t:

   4
  / 
 1   2

Return false.

判断树s是否包含树t

C++（29ms）：

/**
 * 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 == NULL)
            return false ;
        if (isSame(s,t))
            return true ;
        return isSubtree(s->left , t) || isSubtree(s->right , t) ;
    }
    
    bool isSame(TreeNode* s, TreeNode* t){
        if (s == NULL && t == NULL)
            return true ;
        if (s == NULL || t == NULL)
            return false ;
        if (s->val != t->val)
            return false ;
        return isSame(s->left , t->left) && isSame(s->right , t->right) ;
    }
};