题解 | #二叉搜索树的最近公共祖先#

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 p int整型
     * @param q int整型
     * @return int整型
     */
    public int lowestCommonAncestor (TreeNode root, int p, int q) {
        // write code here
        Map<Integer, Integer> map = new HashMap<>();
        int min = Math.min(p, q), max = Math.max(p, q);
        for (int i = min; i <= max; i++) {
            map.put(i, 0);
        }

        search(root, p, map);
        search(root, q, map);

        for (int i = min; i <= max; i++) {
            if (map.get(i) == 2)
                return i;
        }

        return root.val;
    }
    void search(TreeNode root, int num, Map<Integer, Integer> map) {
        while (root.val != num) {
            if (num < root.val) {
                if (map.get(root.val) != null) {
                    map.put(root.val, map.get(root.val) + 1);
                }
                root = root.left;
            } else if (num > root.val) {
                if (map.get(root.val) != null) {
                    map.put(root.val, map.get(root.val) + 1);
                }
                root = root.right;
            }
        }

        map.put(root.val, map.get(root.val) + 1);
    }
}