872. Leaf-Similar Trees

Problem

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

  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].

Solution (Java)

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean leafSimilar(TreeNode root1, TreeNode root2) {
        List<Integer> list1 = new ArrayList<>();
        List<Integer> list2 = new ArrayList<>();
        preOrder(root1, list1);
        preOrder(root2, list2);
        // compare the lists
        if (list1.size() != list2.size()) {
            return false;
        }
        for (int i = 0; i < list1.size(); i++) {
            if (!Objects.equals(list1.get(i), list2.get(i))) {
                return false;
            }
        }
        return true;
    }

    private void preOrder(TreeNode root, List<Integer> list) {
        if (root != null) {
            if (root.left == null && root.right == null) {
                list.add(root.val);
            }
            preOrder(root.left, list);
            preOrder(root.right, list);
        }
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).