Solution.java

/**
 * 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 a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return true;
        } else if (p == null) {
            return false;
        } else if (q == null) {
            return false;
        } else if (p.val != q.val) {
            return false;
        } else {
            boolean isLeftSame = isSameTree(p.left, q.left);
            boolean isRightSame = isSameTree(p.right, q.right);
            return isLeftSame && isRightSame;
        }
    }
}