题解 | 在二叉树中找到两个节点的最近公共祖先

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param root TreeNode类
     * @param o1 int整型
     * @param o2 int整型
     * @return int整型
     */
    public int lowestCommonAncestor (TreeNode root, int o1, int o2) {
        List<Integer> list = new ArrayList<>();
        List<List<Integer>> list2 = new ArrayList<>();
        lowestCommonAncestor2(root, o1, o2, list, list2);
        int result = -1;
        if (list2.size() > 1) {
            List<Integer> integers1 = list2.get(0);
            List<Integer> integers2 = list2.get(1);
            for (int i = 0; i < integers1.size() && i < integers2.size(); i++) {
                if (integers1.get(i).equals(integers2.get(i))) {
                    result = integers1.get(i);
                }
            }
        }
        return result;
    }

    static public void lowestCommonAncestor2(TreeNode root, int o1, int o2,
            List<Integer> list, List<List<Integer>> list2) {
        if (root == null) {
            return;
        }
        if (list2.size() > 1) {
            return;
        }
        list.add(root.val);
        if (root.val == o1 || root.val == o2) {
            List<Integer> newList = new ArrayList<>(list);
            list2.add(newList);
        }
        if (root.left != null) {
            lowestCommonAncestor2(root.left, o1, o2,
                                  list, list2);
        }
        if (root.right != null) {
            lowestCommonAncestor2(root.right, o1, o2,
                                  list, list2);
        }
        list.remove(list.size() - 1);
    }
}