LeetCode - 872. Leaf-Similar Trees

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.

Note:

• Both of the given trees will have between 1 and 100 nodes.

先序遍历，找到叶子节点依次比较

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private List<TreeNode> nodes1 = new ArrayList<>();
    private List<TreeNode> nodes2 = new ArrayList<>();
    public boolean leafSimilar(TreeNode root1, TreeNode root2) {
        frontTraversal(root1, nodes1);
        frontTraversal(root2, nodes2);
        int len1 = nodes1.size();
        int len2 = nodes2.size();
        if (len1 != len2)
            return false;
        for (int i=0; i<len1; i++) {
            if (nodes1.get(i).val != nodes2.get(i).val)
                return false;
        }
        return true;
    }

    public void frontTraversal(TreeNode root, List<TreeNode> nodes) {
        if (root == null)
            return;
        if (root.left != null)
            frontTraversal(root.left, nodes);
        if (root.left == null && root.right == null)
            nodes.add(root);
        if (root.right != null)
            frontTraversal(root.right, nodes);

    }
}