> For the complete documentation index, see [llms.txt](https://jaywin.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jaywin.gitbook.io/leetcode/solutions/1612-check-if-two-expression-trees-are-equivalent.md). # 1612. Check If Two Expression Trees are Equivalent ## Description A [**binary expression tree**](https://en.wikipedia.org/wiki/Binary_expression_tree) is a kind of binary tree used to represent arithmetic expressions. Each node of a binary expression tree has either zero or two children. Leaf nodes (nodes with 0 children) correspond to operands (variables), and internal nodes (nodes with two children) correspond to the operators. In this problem, we only consider the `'+'` operator (i.e. addition). You are given the roots of two binary expression trees, `root1` and `root2`. Return `true` *if the two binary expression trees are equivalent*. Otherwise, return `false`. Two binary expression trees are equivalent if they **evaluate to the same value** regardless of what the variables are set to. **Follow up:** What will you change in your solution if the tree also supports the `'-'` operator (i.e. subtraction)? **Example 1:** ``` **Input:** root1 = [x], root2 = [x] **Output:** true ``` **Example 2:** ![](https://assets.leetcode.com/uploads/2020/10/04/tree1.png) ``` **Input:** root1 = [+,a,+,null,null,b,c], root2 = [+,+,a,b,c] **Output:** true **Explaination:** a + (b + c) == (b + c) + a ``` **Example 3:** ![](https://assets.leetcode.com/uploads/2020/10/04/tree2.png) ``` **Input:** root1 = [+,a,+,null,null,b,c], root2 = [+,+,a,b,d] **Output:** false **Explaination:** a + (b + c) != (b + d) + a ``` **Constraints:** * The number of nodes in both trees are equal, odd and, in the range `[1, 4999]`. * `Node.val` is `'+'` or a lower-case English letter. * It's **guaranteed** that the tree given is a valid binary expression tree. ## ac ```java ```