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