检查两棵二叉表达式树是否等价

/*
 * LeetCode 1612: Check If Two Expression Trees are Equivalent
 * Given two binary expression trees, return true if the two binary trees are equivalent.
 * The equivalent of a binary tree is defined as the trees have the same structure and the same leaf nodes in the same order.
 * 
 * Approach:
 * 1. Perform an in-order traversal of both trees.
 * 2. Collect leaf nodes in the order they appear using streams.
 * 3. Compare the two lists of leaf nodes.
 */

import java.util.*;
import java.util.stream.Collectors;

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}

public class Solution {
    public boolean checkEquivalence(TreeNode root1, TreeNode root2) {
        List<Integer> leaves1 = getLeaves(root1);
        List<Integer> leaves2 = getLeaves(root2);
        return leaves1.equals(leaves2);
    }
    
    private List<Integer> getLeaves(TreeNode node) {
        if (node == null) return new ArrayList<>();
        if (node.left == null && node.right == null) return Arrays.asList(node.val);
        return Stream.concat(getLeaves(node.left).stream(), getLeaves(node.right).stream()).collect(Collectors.toList());
    }
}