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.

isSameTree.java

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(p == null && q == null) {
            return true;
        } else if(p == null || q == null) {
            return false;
        }

        boolean isLeftSame = isSameTree(p.left, q.left);
        boolean isRightSame = isSameTree(p.right, q.right);

        return p.val==q.val && isLeftSame && isRightSame;
    }
}

Can check for condition p.val == q.val before comparing left and right subtrees!