leetcode 872. Leaf-Similar Trees（叶子相似的树）

Consider all the leaves of a binary tree, from left to right order, the values of those leaves form a leaf value sequence.

Example 1:

Input: root1 = [3,5,1,6,2,9,8,null,null,7,4], root2 = [3,5,1,6,7,4,2,null,null,null,null,null,null,9,8]
Output: true

Constraints:
The number of nodes in each tree will be in the range [1, 200].
Both of the given trees will have values in the range [0, 200].

二叉树的叶子序列是叶子节点从左到右组成的序列，问两棵二叉树的叶子序列是否相同

思路：
DFS前序遍历节点，从左到右保存叶子节点到list，最后比较两个list是否相同

    public boolean leafSimilar(TreeNode root1, TreeNode root2) {
        List<Integer> leaves1 = new ArrayList<>();
        List<Integer> leaves2 = new ArrayList<>();
        dfs(root1, leaves1);
        dfs(root2, leaves2);
        
        return leaves1.equals(leaves2);
    }
    
    void dfs(TreeNode root, List<Integer> leaves) {
        if(root == null) return;
        if(root.left == null && root.right == null) {
            leaves.add(root.val);
        }
        dfs(root.left, leaves);
        dfs(root.right, leaves);
    }