872. Leaf-Similar Trees 叶子顺序遍历是否相等

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

For example, in the given tree above, the leaf value sequence is (6, 7, 4, 9, 8).

Two binary trees are considered leaf-similar if their leaf value sequence is the same.

Return true if and only if the two given trees with head nodes root1 and root2 are leaf-similar.

 

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

Example 2:

Input: root1 = [1], root2 = [1]
Output: true

Example 3:

Input: root1 = [1], root2 = [2]
Output: false

Example 4:

Input: root1 = [1,2], root2 = [2,2]
Output: true

Example 5:

Input: root1 = [1,2,3], root2 = [1,3,2]
Output: false

没啥好说的，就是叶子遍历（随便一种遍历顺序）的一个无脑变形罢了……

参考：https://leetcode.com/problems/leaf-similar-trees/discuss/154169/JAVA-very-Easy-understand-solution

class Solution {
    public boolean leafSimilar(TreeNode root1, TreeNode root2) {
        ArrayList<Integer> list1 = new ArrayList();
        ArrayList<Integer> list2 = new ArrayList();
        helper(root1, list1);
        helper(root2,list2);
        if(list1.size() != list2.size()){
            return false;
        }
        for(int i = 0; i < list1.size(); i++){
            if(list1.get(i) != list2.get(i)){
                return false;
            }
        }
        return true;
    }
    private void helper(TreeNode root, ArrayList<Integer> list){
        if(root == null){
            return;
        }
        if(root.left == null && root.right == null){
            list.add(root.val);
        }        
        helper(root.left, list);
        helper(root.right, list);
    }
}