找到二叉树中的距离

/*
 * Leetcode 1740: Find Distance in a Binary Tree
 * 
 * Problem Statement:
 * Given the root of a binary tree and two integer values node1 and node2, 
 * return the distance between the nodes of value node1 and node2 in the tree. 
 * The distance between two nodes is the number of edges on the path from one to the other.
 *
 * Approach:
 * 1. Find the lowest common ancestor (LCA) of the two nodes.
 * 2. Calculate the distance from the LCA to each of the two nodes.
 * 3. Sum these two distances to get the distance between the nodes.
 *
 * This solution utilizes Java Streams to perform the same operations.
 */

import java.util.*;

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

public class Solution {
    public int findDistance(TreeNode root, int p, int q) {
        TreeNode lca = findLCA(root, p, q);
        int d1 = findLevel(lca, p, 0);
        int d2 = findLevel(lca, q, 0);
        return d1 + d2;
    }

    private TreeNode findLCA(TreeNode root, int p, int q) {
        if (root == null || root.val == p || root.val == q) {
            return root;
        }
        TreeNode left = findLCA(root.left, p, q);
        TreeNode right = findLCA(root.right, p, q);
        if (left != null && right != null) {
            return root;
        }
        return Optional.ofNullable(left).orElse(right);
    }

    private int findLevel(TreeNode root, int val, int level) {
        if (root == null) {
            return -1;
        }
        if (root.val == val) {
            return level;
        }
        return Optional.of(findLevel(root.left, val, level + 1))
                       .filter(l -> l != -1)
                       .orElse(findLevel(root.right, val, level + 1));
    }
}