Same Tree

isSameTree.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.

Algorithm:
1. It is a recursive function that check p.left and q.left,
and p.right and p.right, and p.val and q.val
*/

/**
 * 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;
        if(p == null) return false;
        if(q == null) return false;
        if(p.val != q.val) return false;
        
        boolean left = isSameTree(p.left, q.left);
        boolean right = isSameTree(p.right, q.right);
        
        return left && right && (p.val == q.val);
    }
}