100_SameTree.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; }
 * }
 */

//recursive
public class Solution {
    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(q.right, p.right);
    }
}
//iterative
public class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        Stack<TreeNode> stack1 = new Stack<>();
        Stack<TreeNode> stack2 = new Stack<>();
        stack1.push(p);
        stack2.push(q);
        while(!stack1.isEmpty() && !stack2.isEmpty()) {
            TreeNode n1 = stack1.pop();
            TreeNode n2 = stack2.pop();
            if(n1 == null && n2 == null) continue;
            if(n1 == null || n2 == null || n1.val != n2.val) return false;
            stack1.push(n1.right);
            stack2.push(n2.right);
            stack1.push(n1.left);
            stack2.push(n2.left);
        }
        return true;
    }
}