/***
 * Given two binary trees, write a function to check if they are equal or not.
 *
 * Two binary trees are considered equal if they are structurally identical and the nodes have the same value.
 */
/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    // Solution 1: Recursive O(n), O(log n)
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null)
            return true;
        if (p == null || q == null)
            return false;

        return (p.val == q.val) && isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    }
}

add SameTree.java