Same Tree

 Same Tree

Given two binary trees, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

Example 1:

Input:     1         1
          / \       / \
         2   3     2   3

        [1,2,3],   [1,2,3]

Output: true

Example 2:

Input:     1         1
          /           \
         2             2

        [1,2],     [1,null,2]

Output: false

Example 3:

Input:     1         1
          / \       / \
         2   1     1   2

        [1,2,1],   [1,1,2]

Output: false

//
// Algorithm for the recursion:
// 1)
// If one of the node is NULL then return the equality result of p an q.
// This boils down to if both are NULL then return true, 
// but if one of them is NULL but not the other one then return false
// 2)
// At this point both root nodes represent valid pointers.
// Return true if the root nodes have same value and 
// the left tree of the roots are same (recursion)
// and the right tree of the roots are same (recursion). 
// Otherwise return false. 
//

/**
 * 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 isSameTree(TreeNode* p, TreeNode* q) {
        if(p==NULL||q==NULL) return p==q;
        
        if(p->val!=q->val)
            return false;
        return isSameTree(p->left,q->left)&&isSameTree(p->right,q->right);
    }
};

def isSameTree(self, p, q):
    if p and q:
        return p.val == q.val and self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)
    return p is q

public boolean isSameTree(TreeNode p, TreeNode q) {
    if(p == null && q == null) return true;
    if(p == null || q == null) return false;
    if(p.val == q.val)
        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    return false;
}